Muggles' Guide to Harry Potter/Characters/Albus Dumbledore

Overview.
Albus Percival Wulfric Brian Dumbledore was the Headmaster of Hogwarts School of Witchcraft and Wizardry, a Grand Sorcerer decorated with the Order of Merlin, First Class; also Supreme Mugwump of the International Confederation of Wizards and Chief Warlock of the Wizengamot. Ron describes him at one point as "barking." Non-British readers should be aware that this adjective is commonly used in England to modify the word "mad", but without the negative connotations of the word "raving" that is similarly used in the US. Someone who is "barking mad" in the UK is fully functional, but exhibits a very high degree of harmless eccentricity.
According to the author, Dumbledore was born in 1881, and appears to be around 115 years old. 
Dumbledore's wand is Elder, a wood representing banishing, prosperity, protection, renewal, and healing. Elder is also believed to intermingle both good and evil, and its flowers produce a strong odor suggesting death. The wand's inner core contains a thestral tail hair that the author has stated is, "a powerful and tricky substance that can be mastered only by a witch or wizard capable of facing death."
Etymology.
The etymology of the character's name is:
Role in the Books.
Philosopher's Stone.
At Privet Drive, two wizards, Dumbledore and Professor McGonagall arrive to leave Harry, an orphaned infant, with his only remaining family, the Dursleys. Dumbledore places him on the Dursleys' doorstep, along with a letter for the baby's aunt. When Harry Potter is re-introduced to the Wizarding world ten years later, Hagrid tells him that Dumbledore is a powerful wizard and probably the only one the Dark wizard, Lord Voldemort, ever feared.
At the Hogwarts Welcome Feast, Dumbledore rises to say a few words. "And here they are: Nitwit! Blubber! Oddment! Tweak!" Harry wonders aloud if the Headmaster is a bit mad, and Percy Weasley admits he probably is, but also a genius. Dumbledore also issues a warning that, "the third-floor corridor on the right-hand side is out of bounds to everyone who does not wish to die a very painful death." When Harry asks if Dumbledore is serious, Percy responds he must be.
Dumbledore remains a remote figure until Christmas when he discovers Harry gazing endlessly at his dead family's reflections in the Mirror of Erised. Dumbledore explains that the mirror shows only people's desires, not what they truly are. The mirror is moved and Dumbledore requests Harry not look for it again. Dumbledore, apparently able to see through Harry's Invisibility Cloak, suggests there are other ways to be invisible. 
At the Gryffindor vs Hufflepuff Quidditch match, Fred Weasley seems surprised that Professor Dumbledore is attending. Harry, mistrusting Professor Snape as the referee, catches the Snitch quickly, ending the match. Afterwards, Dumbledore tells Harry he is pleased that the Mirror of Erised no longer dominates Harry's thoughts.
Believing Snape is stealing the Philosopher's Stone, Harry, Ron Weasley, and Hermione (also known as the Trio) rush to warn Dumbledore, only to learn he was suddenly called to London. Harry decides to protect the Stone himself, overcoming the final obstacles to reach it and face Voldemort.
In the Hospital Wing, Dumbledore explains he was summoned to London as a ruse, but returned in time to save Harry. Dumbledore is particularly proud of the last protective barrier in the chamber, it involving the Mirror of Erised. He partially explains why events have occurred, though he refuses to say why Voldemort intended to kill Harry.
At the Leaving Feast, Dumbledore awards last-minute House points: fifty points each to Ron and Hermione, and sixty to Harry, for saving the Philosopher's Stone. When Neville Longbottom is awarded ten points for bravery, Gryffindor is catapulted from last place into the lead, winning them the House trophy.
Chamber of Secrets.
Dumbledore disciplines Harry Potter and Ron Weasley after they crash into the Whomping Willow with Mr. Weasley's flying car, sternly warning them that breaking another rule will get them expelled.
Mrs. Norris (Filch's cat) is found Petrified and suspicion falls upon Harry. When Professor Snape suggests Harry knows more than he admits, Dumbledore ignores the accusations and dismisses Harry, Ron, and Hermione without any punishment. 
Colin Creevey is also found Petrified, and Dumbledore concludes that the Chamber of Secrets has been re-opened and Hogwarts is unsafe. Soon after, Justin Finch-Fletchley and Nearly Headless Nick are also Petrified. Circumstantial evidence begins mounting against Harry, but Dumbledore believes he is innocent. He asks Harry if anything is troubling him. Harry, who has been hearing strange voices, responds negatively.
When the diary of T. Riddle shows Harry the events of fifty years previous, Harry sees a much younger Albus Dumbledore in the halls. It is then that we learn that Dumbledore's hair had been auburn fifty years earlier.
Dumbledore accompanies Cornelius Fudge to Hagrid's hut when the Minister arrests him on suspicion of releasing a monster from the Chamber of Secrets. Dumbledore's attempt to dissuade Fudge fails. The twelve school governors, here represented by Lucius Malfoy, have also temporarily relieved Dumbledore as Hogwarts' Headmaster, citing a failure of confidence. 
When Harry enters the Chamber of Secrets to rescue Ginny Weasley, he meets Tom Riddle, a memory stored in a 50-year-old diary who boasts that he caused Dumbledore's expulsion. Harry's loyalty to Dumbledore summons Fawkes, a Phoenix and Dumbledore's animal familiar. Fawkes brings the Sorting Hat that produces Godric Gryffindor's sword. Harry slays the monster and destroys the diary and Tom Riddle's memory.
Upon hearing Ginny was taken into the Chamber of Secrets, the governors recall Dumbledore. Several imply that Lucius Malfoy threatened to curse their families had they not supported Dumbledore's removal. Dumbledore, Mr. Weasley, and Mrs. Weasley await in McGonnagall's office as Harry, Ginny, Ron, and Gilderoy Lockhart are led from the Chamber by Fawkes. Dumbledore helps explain Ginny's unwitting involvement, saying Tom Riddle and Lord Voldemort are the same person, and Voldemort has hoodwinked wizards more powerful than she is.
There are also no consequences for Harry breaking school rules. Dumbledore awards both Harry and Ron 200 house points each and says that they will also recieve special awards to the services to the school awards. Then, Dumbledore assures Harry that, despite similarities to Lord Voldemort, he truly belongs in Gryffindor House, not Slytherin. Dumbledore tells him: "It is our choices, Harry, that show what we truly are, far more than our abilities." Lucius Malfoy is warned that anyone caught aiding the Dark Lord will be severely punished. Dumbledore also gives Harry the encouragement he needs to free Dobby, Malfoy's House-elf who helped Harry.
Prisoner of Azkaban.
At the Welcoming Feast, Dumbledore announces that Dementors are patrolling Hogwarts, hunting the escaped fugitive, Sirius Black. Students are warned that no subterfuge will allow them to bypass the dangerous creatures. He also introduces two new teachers: Rubeus Hagrid (Care of Magical Creatures), and Remus Lupin (Defence Against the Dark Arts).
Draco Malfoy is slightly injured in Hagrid's class. Hagrid is certain Dumbledore will dismiss him. The Trio assure him Dumbledore would never do that.
The fugitive Sirius Black slashes The Fat Lady portrait, apparently an attempt to enter Gryffindor Tower and attack Harry. Dumbledore orders students to the Great Hall for the night, while teachers search the castle and grounds. Snape questions a recent appointment Dumbledore made, though Dumbledore feels certain that no one at Hogwarts would have assisted Black.
During the Quidditch match against Hufflepuff, Harry blacks out when Dementors stream onto the field. Dumbledore slows his fifty-foot fall, then casts a spell that scatters the Dementors.
Over the Christmas holiday, Dumbledore is among a handful staying at the school. While students and staff are having dinner, Professor Trelawney suddenly predicts Lupin's imminent departure, prompting Dumbledore to mildly reply that Remus is probably not in any immediate danger.
At another Quidditch match, Marcus Flint, Draco, Crabbe, and Goyle, disguised as Dementors to scare Harry, are bowled over by Harry's Patronus charm. Professor McGonagall disciplines them, then says Professor Dumbledore is approaching.
The Quidditch final is Gryffindor against Slytherin. Gryffindor wins the match, and Dumbledore presents the Cup to the team.
After Buckbeak is condemned, Dumbledore, Minister for Magic Cornelius Fudge, and the executioner head to Hagrid's hut for Buckbeak's scheduled execution. Hagrid told the Trio that Dumbledore volunteered to be present.
Following the events in the Shrieking Shack, Dumbledore speaks privately to Harry and Hermione in the Hospital Wing. Although Dumbledore now knows Sirius Black is innocent, he says no one will believe two under-aged wizards. Even Remus Lupin, being that a Werewolf will have little credibility with authorities. Dumbledore hints that Hermione and Harry should use the Time Turner, saying that two innocent lives may be spared, then locks them into the hospital wing. Harry understands that Dumbledore intends for them to save Sirius and Buckbeak.
Returning several hours in time, Harry and Hermione, hidden, watch as the execution party enters Hagrid's hut. Dumbledore stalls the proceedings, giving Harry and Hermione enough time to escape with Buckbeak, then rescue Sirius. 
After Black and Buckbeak are safely away, Harry and Hermione meet Dumbledore outside the infirmary, where he has just locked in the "other" Harry and Hermione, who have vanished as the timeline rights itself. Shortly after, Snape bursts in, claiming Harry and Hermione aided Black's escapes, though Dumbledore insists they were in the Hospital Wing.
Snape reveals that Lupin is a Werewolf, forcing him to resign. While packing, Lupin tells Harry that Harry's father's Animagus form was a stag, the same shape as Harry's Patronus. After Lupin's departure, Dumbledore tells Harry that Sirius admitted that he and James Potter were unregistered Animagi. Harry believed it was his father's Patronus, not his own, that scattered the Dementors. Dumbledore says that as long as they are remembered, those who have died never truly leave. "Make no mistake — Prongs (James Potter) rode again last night."
Goblet of Fire.
At the Hogwarts' Welcome Feast, Dumbledore introduces Professor Alastor Moody, the new Defence Against the Dark Arts teacher. Harry notices Moody only drinks from a hip flask. Dumbledore also announces Hogwarts is hosting the Triwizard Tournament, an inter-school competition that also includes the Beauxbatons Academy and Durmstrang Institute. Students under 17 are excluded from the tournament.
During Defense Against the Dark Arts class, Professor Moody overrules Hermione's objections to him demonstrating the three Unforgivable Curses, saying Dumbledore wants students to recognize them. Though disapproving, Hermione remains for the demonstration, despite Moody's offer that any student can be excused.
Madam Maxime, the Beauxbatons Headmistress, and Igor Karkaroff, Durmstrang's Headmaster arrive with their students for the Tournament. Following a feast, Dumbledore introduces Ludo Bagman and Bartemius Crouch, who are Triwizard Tournament judges, along with the three Headmasters. Dumbledore explains that eligible students can enter the tournament by placing their name into the Goblet of Fire, but once a contestant enters, they are unable to withdraw. The Goblet will select one Champion from each school. 
At the Hallowe'en Feast, Dumbledore announces the Champions as the Goblet selects them: for Durmstrang, Viktor Krum. Fleur Delacour is chosen for Beauxbatons. The Hogwarts Champion is Cedric Diggory. But Dumbledore is stunned when the Goblet also chooses Harry Potter. Although Harry insists he never entered, Crouch rules that he is magically bound to compete. Dumbledore suspects there is a plot against Harry, while the other school Heads believe he cheated. Noticing Crouch's ill appearance, Dumbledore invites him to stay at the castle, but Crouch declines. 
At the Weighing of the Wands ceremony, Dumbledore rescues Harry from Daily Prophet reporter, Rita Skeeter after she traps Harry for an interview. Dumbledore pointedly remarks about Skeeter's latest unflattering story about him. Dumbledore stays for a photo session following the ceremony.
For the First Task. Harry captures a golden dragon egg in the shortest time. Dumbledore scores him a nine out of ten points.
During the Yule Ball, Dumbledore mentions to Karkaroff that he once discovered a room filled with chamber pots, illustrating how no one can know every Hogwarts secret. Dumbledore also dances, rather awkwardly but without embarrassment, with the exceedingly tall Madame Maxime.
Rita Skeeter publishes a scurrilous story revealing Hagrid's half-Giant ancestry. Hagrid, mortified, retreats into seclusion. When Hermione, Harry, and Ron go to Hagrid's hut to console him, they find Dumbledore there. Dumbledore advises Hagrid that he must ignore the press, and relates how his own brother was once pilloried in the press, then simply went on as before. Dumbledore orders Hagrid to return to work on Monday.
After Moody prevents Argus Filch and Professor Snape from catching Harry out after hours, Moody tells him that Dumbledore believes in second chances, whereas he and Mr. Crouch do not. Harry wonders what Snape, a suspected former Death Eater, had done to deserve a second chance.
At the Second Task, Dumbledore is present when Harry surfaces from the lake with his rescued "hostages." Dumbledore determines that Harry had arrived at the hostage site first, but remained to ensure all were rescued, putting him over the time limit. Harry is awarded extra points for noble behaviour. 
After surveying the Third Task's maze, Viktor Krum and Harry are talking when a disheveled Mr. Crouch suddenly appears, rambling incoherently, then demanding to see Dumbledore. Harry returns with Dumbledore, only to find Crouch missing and Krum unconscious. Dumbledore revives Krum, then summons Hagrid, telling him to find Karkaroff. Moody suddenly appears, and Dumbledore has him search for Crouch. Dumbledore orders Harry to remain in his dorm until morning; any messages can wait until then. Harry wonders how Dumbledore knew he was planning to write Sirius.
After experiencing another vision, Harry heads to Dumbledore's office. Outside, he overhears Dumbledore, Cornelius Fudge, and Professor Moody discussing Bertha Jorkins and Bartemius Crouch disappearing. Dumbledore discounts a suggestion that Madam Maxime was involved. Moody detects Harry's presence, and he is invited inside. Dumbledore tells him to remain there until he returns. 
While waiting, Harry peers into a stone basin containing a shimmering substance. Suddenly he finds himself seated alongside Dumbledore in a courtroom, and realizes he is inside a memory. It is Igor Karkaroff's hearing where he agrees to name Death Eaters in exchange for leniency. The image shifts to Ludo Bagman's trial for passing Ministry secrets to a Death Eater. Finally, four people stand accused of torturing Frank and Alice Longbottom into insanity. Bartemius Crouch, the prosecutor, sentences his own son, Barty Jr. to Azkaban prison. A second Dumbledore appears and returns Harry to the office. Dumbledore identifies the stone basin as a Pensieve, a useful place to store memories and study thought patterns.
Dumbledore concludes Harry's summer dream was no ordinary one, and believes Harry's scar hurts whenever Voldemort is nearby or feels intense emotions. Dumbledore also reveals that Neville's parents, Frank and Alice Longbottom, never regained their sanity and permanently reside at St. Mungo's Hospital. Dumbledore requests Harry keep this confidential, it is for Neville to tell others. Also, neither Snape or Ludo Bagman has been connected with anything Dark since the trials; Finally, Dumbledore wishes Harry luck in the Third Task.
Sirius writes Harry that he should be safe under Dumbledore's protection. At the Third Task, Dumbledore watches as the four Champions enter the maze and is waiting as Harry returns, bearing Cedric Diggory's body. Amid the confusion, he orders Harry to remain where he is; but Harry, distraught and confused, is led away by Moody. Shortly, Dumbledore, McGonagall, and Snape burst into Moody's office, stunning Moody, an imposter. Dumbledore has Snape fetch Veritaserum, a truth potion, then frees the real Moody trapped in a trunk. The imposter is Barty Crouch, Jr., disguised by Polyjuice Potion. Dumbledore knew the real Moody would never have moved Harry after Dumbledore told him to stay put. Barty confesses the Triwizard Cup was a Portkey that transported Harry (and also Cedric Diggory) to Lord Voldemort to be murdered.
Sirius is waiting as Harry and Dumbledore arrive in the Headmaster's office. Harry is tired and weak, but Dumbledore wants him to relate what happened after touching the Triwizard Cup. Dumbledore seems particularly interested that Voldemort used Harry's blood to resurrect his body. Dumbledore also explains that when two wands sharing a common core are forced to duel, the Priori Incantatem effect forces one wand to disgorge its most recent spells; that is why Harry saw his parents' images. Dumbledore and Sirius escort Harry to the Hospital Wing, where Mrs. Weasley, Bill Weasley, Ron, and Hermione are waiting.
When Dumbledore returns to the infirmary, an angry McGonagall reports that a Dementor has sucked out Barty's soul on Fudge's order. Fudge defends his actions, claiming Barty believed he was acting on Voldemort's behalf, therefore his testimony would be suspect. Dumbledore maintains Barty "was" following Voldemort's direct orders, though Fudge disputes Harry's account that Voldemort has returned. Fudge storms out, the two men's differences permanently dividing them.
Dumbledore orders Bill Weasley to report everything that has happened to his father and asks McGonagall to bring Hagrid and Madame Maxime to his office. He requests that Sirius and Snape call a truce and work together, then sends Sirius to gather "the old crowd": Remus Lupin, Mundungus Fletcher, and Arabella Figg. Snape is sent on the mission he and Dumbledore previously discussed. Hagrid and Madam Maxime also have a secret mission.
When Harry is discharged from the Hospital Wing, Ron and Hermione tell him that Dumbledore addressed the school about what happened. Mrs. Weasley asked Dumbledore if Harry could spend the summer at the Burrow, but Harry must first stay at Privet Drive.
At the Leaving Feast, Dumbledore gives a tribute to Cedric Diggory, explaining that Lord Voldemort murdered him. The Ministry would object to him revealing this, but truth is better than lies. He also toasts Harry for risking his life to return Cedric's body. Finally, addressing Beauxbatons and Durmstrang, he says they will always be welcome at Hogwarts, as all must stand together against dark forces.
Order of the Phoenix.
During the summer, Harry and Dudley are attacked by Dementors that Harry repels with a Patronus. Dumbledore rushes to the Ministry of Magic to intercede in any hasty punitive action against Harry for using underaged magic. A Howler message to Petunia Dursley, likely from Dumbledore, admonishes her after she attempts to eject Harry from the Dursley house. Shaken, she tells Vernon that Harry must stay.
Harry is quickly moved to the Order of the Phoenix Headquarters at Number 12, Grimmauld Place where he is re-united with Sirius Black. Ron and Hermione are also there, but Harry is vexed they never responded to his queries about Voldemort, though Dumbledore ordered them to reveal nothing; they actually know little more than Harry. Harry is also perturbed after Dumbledore selects Ron (and also Hermione) as a Gryffindor prefect, but not him. Harry learns that the Order is a secret group fighting Voldemort; they remain undercover because the Ministry of Magic officially claims Voldemort never returned. Dumbledore, who has publicly stated that Voldemort was resurrected, has been openly ridiculed and removed from many important Wizarding posts.
Harry is later allowed to ask questions about Voldemort and the Order. Voldemort, he is told, remains unseen as he regains strength and gathers more followers. Harry foiled Voldemort's plan by escaping the cemetery and informing the one person Voldemort least wanted to know he had returned: Dumbledore. The Order's Headquarters is protected by the Fidelius charm, and Dumbledore is the Secret-keeper.
Shortly before Harry's hearing at the Ministry, Dumbledore visits Headquarters without speaking to Harry, upsetting him. At the hearing, Dumbledore appears as a surprise witness, defending Harry brilliantly, citing that underage wizards are allowed to use magic in self defence. He introduces Mrs. Figg, a Squib, who has been secretly guarding Harry at Privet Drive. She testifies that Dementors attacked Harry. After defusing Fudge's accusations, Dumbledore suggests that someone within the Ministry must have sent the Dementors. When Harry is exonerated, Dumbledore immediately departs without a word to Harry, leaving Harry further frustrated.
At the Hogwarts Welcome Feast, Dumbledore gives his customary speech, then introduces Dolores Umbridge, a Ministry official and spy, as the new Defence Against the Dark Arts instructor. She inappropriately rises to give her own speech, though only Hermione seems able to follow her deadly dull words. Harry learns later that some wizard families were concerned about their children returning to Hogwarts, including Seamus Finnigan's parents, who feel Dumbledore may be "losing it" by insisting Voldemort has been resurrected.
Harry remains upset that Dumbledore continually avoids him. Hermione suggests that Dumbledore has probably not mentioned Hagrid's absence to avoid calling attention to it, and Angelina Johnson thinks Dumbledore's influence allowed the Gryffindor Quidditch team to reform after Umbridge's Educational Decree Number Twenty-Four banned it. Sirius tells Harry, Ron, and Hermione that Umbridge was foisted on the school because Cornelius Fudge suspects Dumbledore is training students to create a secret wizard army to overthrow the Ministry. That is why Umbridge's classes are deliberately ineffectual. In response, Harry secretly forms his own defensive arts group named, "Dumbledore's Army". When Dobby suggests they use the Room of Requirement, Harry remembers Dumbledore mentioning it at the Yule Ball. When Hagrid returns, he tells Harry, Hermione, and Ron that Dumbledore sent him and Madame Maxime to secretly contact the Giants and persuade them to join Dumbledore.
Just before Christmas, Harry has a vision that Arthur Weasley is being attacked by a snake. Without looking directly at Harry, Dumbledore questions him about the attack. Dumbledore sends two Headmaster portraits to investigate and has Professor McGonagall bring the other Weasley children to his office. Word is sent to Sirius at Headquarters that guests are arriving before Dumbledore transports Harry and the Weasley children to Grimmauld Place by Portkey. As Dumbledore and Harry briefly make eye contact, Harry feels the snake welling within, ready to strike the Headmaster.
Dumbledore never appears at Headquarters during the holidays, and, fearing Voldemort is possessing him, Harry decides to leave to protect the Order. Phineas Nigellus' portrait delivers Dumbledore's urgent message stating, "Stay where you are." Harry complies. Soon after, Severus Snape arrives with unwelcome news: Dumbledore wants Snape to teach Harry Occlumency. No further explanation is given.
Harry "sees" Voldemort discussing a plan with a Death Eater, who says Avery's idea would not work. Still resentful over Dumbledore ignoring him, Harry childishly refuses Ron's suggestion that he report his vision to Dumbledore
Dumbledore countermands Umbridge's dismissing Professor Trelawney by allowing her to remain in the castle. He invokes his power to fill the vacancy himself, then introduces Firenze, a Centaur, as the new Divination teacher, further infuriating an already livid Umbridge.
Umbridge dispatches her Inquisitorial Squad (Slytherin students like Draco Malfoy) to capture Dumbledore's Army members. Only Dobby's timely tip-off allows all members, except Harry, to escape. Harry is ushered to the Headmaster's office where Dumbledore, along with Professor McGonagall, Umbridge, Cornelius Fudge, and Percy Weasley are waiting. Also present are two Aurors: Dawlish and Kingsley Shacklebolt, who is actually an Order of the Phoenix member. 
Dumbledore disputes Umbridge's claims that Harry held an illegal meeting at the Hog's Head Inn, noting it occurred before her Educational Decree took effect. Umbridge provides a witness to additional meetings, but a discreet Memory charm cast by Kingsley leaves the girl befuddled. Exasperated, Fudge then claims that a membership roster titled, "Dumbledore's Army" proves Dumbledore is creating a secret army, to which Dumbledore pleasantly concurs. As the Aurors attempt to arrest Dumbledore, they, Fudge, and Umbridge are knocked unconscious amid flashing Phoenix fire. Dumbledore escapes with Fawkes.
Months pass without any word from Dumbledore, while the Headmaster's office remains magically sealed off, preventing anyone but a true Headmaster from entering. Harry suspects Dumbledore is secluded inside. When Umbridge catches Harry using the Floo network in her office to call Sirius, Hermione claims they were contacting Dumbledore about a secret weapon he ordered them to build. They lead her to the non-existent weapon in the Forbidden Forest, where angry Centaurs carry Umbridge away.
Dumbledore reappears at the climactic battle at the Ministry of Magic and captures nearly all the Death Eaters, except Bellatrix Lestrange. Voldemort arrives and he and Dumbledore fiercely duel; Voldemort possesses Harry, whose overwhelming feelings of love, friendship, and loyalty drive out Voldemort. Ministry wizards and Aurors, including Fudge, arrive, seeing Voldemort before he and Bellatrix escape. Dumbledore sends Harry to his office by Portkey, then grants Fudge a half-an-hour's explanation before he returns to Hogwarts.
Reinstated as Headmaster, Dumbledore comforts Harry, who is distraught over Sirius' death. Dumbledore admits he made mistakes, such as never revealing a prophecy to Harry stating that either Harry or Voldemort must die at the hand of the other. He had avoided Harry to prevent Voldemort from probing Harry's mind about Dumbledore and the Order of the Phoenix. Dumbledore also explains he did not choose Harry to be a prefect because, "I felt... that you already had... enough responsibilities to be going on with."
Dumbledore regains his posts in the Wizengamot and the International Confederation of Wizards. He also fetches Dolores Umbridge from the Centaurs; Umbridge, traumatized and unable speak, eventually flees the school's Hospital Wing.
Half-Blood Prince.
Dumbledore arrives at Privet Drive to collect Harry, who is delighted to be leaving his detested home after only a fortnight. Harry has inherited Sirius' property, including the house at Grimmauld Place, Kreacher, and Buckbeak, but a charm may exist that magically leaves everything to Bellatrix Lestrange. Dumbledore summons Kreacher, who immediately obeys Harry's command, proving Harry is Sirius' heir. Kreacher is then sent to work in the Hogwarts kitchens. Dumbledore chastises the Dursleys for over-indulging Dudley while abusing Harry, saying he had requested they treat Harry as their own. After departing, Harry notices Dumbledore's blackened and dead-looking hand, but Dumbledore defers an explanation.
Dumbledore must also recruit a new teacher, and he and Harry Apparate to Budleigh Babberton, a tiny village. Inside a small house, Harry and Dumbledore discover destruction. Dumbledore pokes an overturned armchair which springs into the fat, bald wizard, Horace Slughorn, who is hiding from Voldemort. Dumbledore surmised Slughorn staged the scene because there was no Dark Mark over the house. When Slughorn declines Dumbledore's offer to resume his old teaching post, Dumbledore briefly leaves Harry alone with Slughorn, who is fascinated by the famous boy wizard. Upon returning, Dumbledore makes one final offer, but, seemingly defeated, he and Harry prepare to leave. Slughorn suddenly accepts the post.
Apparating to The Burrow, Dumbledore draws Harry aside, suggesting he tell Ron and Hermione about the Prophecy. He also requests that Harry always carry his Invisibility Cloak with him during the coming year, and says they will be having private lessons.
At the Arrival Feast, Dumbledore announces two new staff appointments: Horace Slughorn is the new Potions master, while Professor Snape becomes the new Defence Against the Dark Arts instructor. With Voldemort's reappearance, new protective spells have been placed around the school; Dumbledore asks for the students' patience and cooperation.
Rather than studying magic, Harry and Dumbledore will instead review and extend Dumbledore's research into Voldemort. Peering into the Pensieve, they view memories belonging to Bob Ogden, a Ministry representative arriving at the Gaunt home. Ogden is attacked by Morfin Gaunt, who speaks to his father, and watches the byplay between them and Merope Gaunt, as the Muggle Tom Riddle rides by. Dumbledore explains that Marvolo Gaunt may be Tom Riddle Jr.'s (Voldemort) grandfather. Merope is Voldemort's mother, and the handsome Muggle is his father, Tom Riddle. The homely Merope magically ensnared Riddle Sr., though, for reasons unknown, the enchantment lapsed, and he abandoned her. Merope died soon after Tom, Jr's birth. Dumbledore asks Harry that this information go no further than Ron and Hermione. Harry notices a broken ring on Dumbledore's desk is the same one in Ogden's memory. It is the signet of the Peverells, an old pure-blood Wizarding family. 
Dumbledore is absent until mid-October; when he returns, he tells Harry that Professor Snape, experienced with Dark magic, has done everything possible for Katie Bell, who was injured by a cursed necklace apparently intended for someone else. Harry suspects Draco Malfoy was behind the attack, and Dumbledore assures him that Draco will be investigated. He also reassures Harry that Mundungus Fletcher will never steal another item from Grimmauld Place. Returning to their lesson, Dumbledore says Merope Gaunt, alone and pregnant, went to London and sold some valuables to survive, apparently unable or unwilling to use magic. In the Pensieve, Caractacus Burke of Borgin &amp; Burke's gloats over purchasing Slytherin's locket for ten Galleons. Harry is outraged by Burke's avarice. Next, the younger Dumbledore visits the orphanage where Tom Riddle, Jr. lives. The matron recounts Tom's unsavoury behaviour and says that two children, absent with Tom at a seaside outing, returned terrified.
Tom is initially suspicious upon meeting Dumbledore, though the professor convinces the boy he is a wizard and can attend a school for magic. As proof, Dumbledore performs magic. Tom is offered financial support, but he insists on finding Diagon Alley by himself. Dumbledore, worried about Tom Riddle's cruelty, ambition, thieving, and his reaction to learning he was a wizard, resolved to closely watch him. Even then, Tom set himself apart, apparently friendless. Tom also liked collecting trophies. 
Dumbledore is flattered when Harry, having angrily rebuffed new Minister for Magic Rufus Scrimgeour's attempt to recruit him as a Ministry poster boy, considers Scrimgeour's slur that he is "Dumbledore's man", as a compliment. Harry also relates a conversation between Snape and Draco Malfoy, in which Draco refused Snape's assistance, even though Snape is sworn to help him. Dumbledore assures Harry he trusts Snape. 
They proceed to memories about Riddle's Hogwarts days when Tom was gathering a core group, later loyal Death Eaters. The first memory shows Tom appearing in the Gaunt shack. After learning Tom's identity, Morfin tells him about his mother, Merope, and Muggle father, Tom Sr. Everything suddenly goes black. When Morfin awoke, the entire Riddle family was dead via a spell cast by Morfin's wand, and the Peverell ring was missing.
The second memory shows the much younger Professor Slughorn and his "Slug Club" group, including Tom Riddle, now about fifteen and wearing the Peverell ring. When Tom asks about Horcruxes, the memory becomes cloudy and only Slughorn's voice is heard. This memory has been altered, and Dumbledore tasks Harry with retrieving Slughorn's unedited version. Later, Hagrid tells Harry he overheard Dumbledore and Snape having a disagreement. Snape seemed reluctant about something he agreed to do. Dumbledore firmly reminded Snape he had given his word. Dumbledore also mentioned Snape's investigations into Slytherin, which Hagrid assumes is about the cursed necklace.
At their next meeting, Dumbledore is disappointed by Harry's failure to obtain Slughorn's memory. Without it, there will be little point in proceeding. Harry makes it his top priority. The lesson continues as they now enter a realm of deep speculation. The first memory belongs to Hokey, a House-elf belonging to Hepzibah Smith. Hepzibah claims to be Helga Hufflepuff's descendent. Tom Riddle, now a buyer for Borgin &amp; Burke's, makes Hepzibah an offer for Helga Hufflepuff's cup and Salazar Slytherin's locket. Tom has difficulty releasing the locket, particularly after hearing Burke paid some poor witch a pittance for it. Dumbledore says Hepzibah died two days later. Hokey, believing she had accidentally poisoned her mistress, was punished, but Hepzibah's treasures were never found. At about the same time, Riddle left Borgin &amp; Burke's.
The second memory is Dumbledore's, ten years later. Riddle is seeking the Defence Against the Dark Arts post. He was previously declined a teaching position by then Headmaster, Armando Dippet, citing his inexperience. Dumbledore, noting Tom's changed appearance, refuses to use his new name (Lord Voldemort), and knows about his Death Eaters and recent activities. Distrusting Tom's motives, Dumbledore rejects his application. Ever since any Defence Against the Dark Arts teacher has never lasted longer than one year.
After sipping some good luck potion, Harry obtains Slughorn's memory and takes it to Dumbledore. They revisit the Slug Club memory. Slughorn is describing to Tom Riddle how a soul can be split by committing murder; the torn fragment can then be encased in a physical object, tying it to the Earth, ensuring immortality. Slughorn is horrified when Riddle suggests splitting the soul multiple times. And is not seven the most magical number?
Dumbledore speculates that Voldemort divided his soul into seven pieces, six Horcruxes in all, with the damaged portion left in Voldemort's body. As long as any Horcrux remains, Voldemort is immortal. Dumbledore believes the Horcruxes are unique objects. Two have been destroyed: Tom Riddle's diary and the Peverell ring. Dumbledore reveals he injured his hand while destroying the ring. Only his skill and Snape's timely action contained the damage. Dumbledore believes Hufflepuff's cup and Slytherin's locket are Horcruxes, and one will likely be a Gryffindor or Ravenclaw artifact. The last one may be Voldemort's snake, Nagini. Voldemort's soul may be too shredded for him to detect when a Horcrux is destroyed. If all his Horcruxes are eliminated, then Harry can kill Voldemort. It is Harry's capacity to love and make choices that gives him power Voldemort lacks. Dumbledore tells Harry he can accompany him when he locates another Horcrux. 
Harry becomes enraged when he learns it was Snape who revealed Trelawney's prophecy's second half to Voldemort, but Dumbledore reiterates that he trusts Snape. He then says he has found another Horcrux. Harry can accompany him but must promise absolute obedience. Harry reluctantly agrees.
Dumbledore and Harry Apparate to the same seaside cliff young Tom Riddle took his two fellow orphans, terrifying them. Inside a cave, Dumbledore offers his blood to open a hidden doorway leading into another cavern containing a lake; a green glow is at the lake's center. Unable to Summon the Horcrux, Dumbledore and Harry set off in a tiny boat. Dead bodies are floating in the water, which Dumbledore assures Harry are harmless as long as they are only floating.
The green light is emanating from a basin on a tiny island. A potion inside covers the locket, which Dumbledore guesses can only be removed by drinking the liquid. He makes Harry promise to force him to drink everything. The potion's effect is horrific, causing intense pain, terrible memories, and intense raving as Dumbledore pleads with Harry to kill him. The locket is retrieved, and as Harry draws water from the lake for Dumbledore to drink, he is seized by Inferi. Dumbledore revives enough to conjure fire to repel the creatures, freeing Harry. 
Making it back to the cliff, Dumbledore Apparates them to Hogsmeade before collapsing. Before Harry can fetch Snape as Dumbledore requests, Madam Rosmerta appears, saying the Dark Mark is over the school. Summoning brooms from a pub, Harry and Dumbledore fly to the Astronomy Tower, Dumbledore muttering charms to allow them passage through the protective spells.
Atop the Tower, Dumbledore, hearing someone approach, Petrifies Harry under his Invisibility Cloak to protect him. Draco Malfoy appears and disarms Dumbledore. But distraught and frightened, he is unable to complete his task - to kill Dumbledore. Draco has helped Death Eaters enter the school through a secret passage. Four Death Eaters, then Snape, suddenly appear. Fulfilling his Unbreakable Vow to Draco's mother, Snape blasts Dumbledore with a killing curse, catapulting his body over the wall.
The school remains open until after Dumbledore's funeral, allowing all students to pay their last respects. Many Wizarding denizens attend the funeral, then a white tomb magically appears, surrounding Dumbledore's body. 
Everyone, including Harry, believes Snape a traitor, though Dumbledore's trust in him never wavered. It is unclear whether Snape actually betrayed Dumbledore or was acting under unknown circumstances. Regardless, Harry vows to destroy both Voldemort and Snape. Harry also discovers that someone whose initials are R.A.B. replaced the real Horcrux with a fake locket.
Deathly Hallows.
Although Dumbledore is dead, his influence lives on. His obituary in the "Daily Prophet", written by his old friend, Elphias Doge, states that Dumbledore's father, Percival, was sentenced to Azkaban for attacking three Muggle children. Albus overcame the notoriety by excelling at Hogwarts, while his brother, Aberforth, preferred settling arguments by dueling rather than debate. As Albus and Elphias were about to embark on a world tour, Dumbledore's mother, Kendra suddenly died, forcing Albus to support the family. Shortly after, Albus' younger sister, Ariana also died. Following these tragedies, Albus went on to many notable achievements, including defeating the Dark wizard Gellert Grindelwald.
A teaser in the "Daily Prophet" about Rita Skeeter's new book suggests that Dumbledore dabbled in Dark magic, that Ariana was a Squib, and Aberforth and Albus were estranged. It also implies that Dumbledore and Grindelwald's epic duel was something other than it seemed, and hints that Dumbledore's relationship with Harry may have been less than savoury. Harry is stunned and outraged by these revelations, but realizes he hardly knew Dumbledore; their conversations were mostly about Harry. 
The Order has moved its Headquarters from Grimmauld Place to The Burrow. As Dumbledore was the Secret-Keeper, his death enables any person, including Snape, who knew Grimmauld's location to divulge its location to anyone.
As Harry, Ron, and Hermione prepare for Dumbledore's mission, Hermione comments on how easily she Summoned the Dark magic books from Dumbledore's study, almost as if Dumbledore intended for her to retrieve them. Harry relates Slughorn's memory regarding Tom Riddle and his Horcruxes, and they wonder how Dumbledore destroyed the ring Horcrux. Harry has packed a shard from the broken two-way mirror Sirius gave him. In it, Harry continually glimpses a blue flash, similar to Dumbledore's eye colour. 
While at the Burrow, Harry "sees" Voldemort's thoughts. Hermione urges him to close the connection, but Dumbledore believed Voldemort found Harry's emotions to be so disturbing to him (at the end of "Harry Potter and the Order of the Phoenix"), that he is unlikely to possess him again.
Minister for Magic Rufus Scrimgeour arrives to present Harry, Ron, and Hermione their bequests from Dumbledore's will, but only after the Ministry closely examined them. Ron receives a Deluminator, a magical device for extinguishing lights, (seen in chapter 1 of "Harry Potter and the Philosopher's Stone"). For Hermione, an old edition of "The Tales of Beedle the Bard". And to Harry, the Golden Snitch from his first Quidditch match. Dumbledore also bequeathed Harry the Sword of Gryffindor, but Scrimgeour insists Dumbledore was never its owner; it remains at Hogwarts. Hermione later speculates that Scrimgeour probably wanted Harry to hold the Snitch because it has a "flesh memory", apparently expecting it to react when Harry touched it. Harry reminds her that he caught the Snitch in his mouth. Pressing the gold ball to his lips, Dumbledore's handwriting appears on it reading, "I open at the close." Its meaning leaves the Trio mystified.
At Bill and Fleur's wedding, Harry asks Elphias Doge about Skeeter's claims. Elphias insists Ariana Dumbledore was not a Squib, only ill, but the Weasleys' Auntie Muriel claims she knows that Ariana was never a patient at St. Mungo's. Muriel also mentions that the family moved to Godric's Hollow and that Aberforth and Albus got into a fist fight at Ariana's funeral. 
When Death Eaters attack The Burrow, the Trio escapes to Number 12, Grimmauld Place. There they are greeted by Dumbledore's dusty simulacrum, one of the curses placed on the old Headquarters to prevent Severus Snape and Death Eaters from entering.
Remus Lupin arrives and informs the Trio that the Ministry wants Harry for questioning related to Dumbledore's death, while the "Daily Prophet" reports that Severus Snape has been appointed Headmaster of Hogwarts. Alecto Carrow and Amycus Carrow are the new Muggle Studies and Defence Against the Dark Arts teachers. The Carrows were among the Death Eaters present when Dumbledore died. 
Harry, Ron, and Hermione infiltrate the Ministry of Magic to retrieve Slytherin's Locket Horcrux from Dolores Umbridge. Once inside, Harry recognizes Yaxley, a Death Eater who was present when Dumbledore was killed. While searching Umbridge's office, Harry spots Rita Skeeter's book. The Trio escapes with the Locket Horcrux, but are forced to abandon Grimmauld Place and go on the run. 
Ron maintains Dumbledore would have known if a Horcrux was hidden at Hogwarts, though Harry says Dumbledore never claimed to know all the school's secrets. The Trio learns from Phineas Nigellus' portrait that Dumbledore used Gryffindor's Sword to destroy the ring Horcrux, though the sword that is now at Hogwarts is fake and the real sword's location is unknown. Harry feels angry that Dumbledore left him so little information.
A hand-drawn mark found inside "The Tales of Beedle the Bard" that Dumbledore left Hermione is the same symbol Xeno Lovegood was wearing. It is also Grindelwald's mark. Meanwhile, Harry and Hermione agree that the Sword of Gryffindor could be hidden in Godric's Hollow, possibly left with Bathilda Bagshot, a noted historian. They Apparate to Godric's Hollow. In a church cemetery, Hermione finds the same symbol on Ignotus Peverell's tombstone.
In Skeeter's book, Harry and Hermione find a photo of the teen-aged Dumbledore and his friend, Gellert Grindelwald. In the chapter, "The Greater Good". Skeeter writes that Dumbledore returned to Godric's Hollow to head the family, though many residents saw little evidence of that. Aberforth ran wild, and Ariana stayed hidden. That same summer, Bathilda Bagshot took in her grand-nephew, Gellert Grindelwald, a brilliant student who was expelled from Durmstrang. He and Albus became close friends. In a letter to Gellert, Albus agrees Wizards should dominate Muggles, if it is for "the greater good," but wizards must rule responsibly. Skeeter claims Dumbledore planned to establish wizards' rule over Muggles, contradicting his later stance supporting Muggle-born wizards and protecting Muggles' rights.
Soon after, Dumbledore and Grindelwald acrimoniously parted, possibly due to Ariana's sudden death. Aberforth blaming Albus for Ariana's demise also seemed connected to Albus and Gellert's relationship. Grindelwald went on to terrorize the European wizard world; for five years, Dumbledore ignored pleas for help before challenging and defeating Grindelwald. Unanswered questions remained: Had Dumbledore's prior relationship with Grindelwald delayed his taking action? If Ariana was a Squib, was her death accidental or a first attempt at implementing The Greater Good?
These revelations cause Harry to suffer another loss: his faith in Dumbledore, who he once believed embodied only goodness and wisdom. Hermione discredits Rita Skeeter's account and doubts that Dumbledore would oppress Muggles, despite what he professed at age seventeen. Instead he chose to fight evil his entire life. Hermione surmises Harry is really angry because Dumbledore never shared this information, which Harry acknowledges that might be true, but he wonders how Dumbledore could leave him such a mess. He is also left doubting Dumbledore's love for him.
Xenophilius Lovegood tells the Trio about the Deathly Hallows and the three Peverell brothers. Harry guesses that his father's Invisibility Cloak that Dumbledore once borrowed is a Hallow, and the Ring Horcrux was a Peverell artifact, which Harry suspects may be hidden inside the Golden Snitch. Hermione and Ron, worried Harry is becoming obsessed with the Hallows, urge him to remain focused on only destroying the Horcruxes.
Harry ponders whether Dumbledore deliberately made everything so difficult to give Harry time to work things out. Meanwile, Mr. Ollivander tells Harry that the Elder Wand, a Hallow, is apparently undefeatable, though its owner is not. While its history suggests it was passed from wizard to wizard through murder, Ollivander claims only disarming its master is necessary.
Harry realizes that Voldemort seeks the Elder Wand. Grindelwald stole it from Gregorovitch, using it to conquer Europe until Dumbledore defeated him; Dumbledore possessed it ever since. Meanwhile, Harry watches through Voldemort's eyes as he removes the Elder Wand from Dumbledore's tomb. Harry wonders if only hunting for the Horcruxes, as Dumbledore wanted, is the correct course. Harry also "sees" Voldemort's violent reaction to learning that the Trio obtained another Horcrux. Voldemort believes Dumbledore, who never trusted him, must be involved. He is uncertain now if he can feel his Horcuxes being destroyed, and goes to check on another.
Arriving in Hogsmeade, Harry, Hermione, and Ron are cornered by Death Eaters, but Aberforth Dumbledore pulls them safely into his pub. Harry spies the twin to Sirius' mirror—Aberforth has been watching them through it. Aberforth questions Albus' mission, asking if Albus had been completely honest or if Harry ever wondered why three young, unqualified wizards were entrusted with such a dangerous mission. Harry, wracked by doubt, is unable to answer; Aberforth scoffs that Albus learned secrecy at their mother's knee.
Aberforth reveals the truth about his family's past. Young Ariana was injured by Muggle boys who saw her performing magic, leaving her unable to control her powers. Their father, Percival, attacked the boys in retaliation, and, refusing to defend himself, was sentenced to Azkaban, where he died. Their mother, Kendra, moved the family to Godric's Hollow and kept Ariana's condition hidden, spawling rumours she was a Squib.
Ariana's care fell upon Kendra and Aberforth, while Albus immersed himself in his studies, confining himself to his room when at home. When Ariana accidentally killed Kendra with an uncontrolled magical outburst, Albus returned home to care for the family, just as Grindelwald turned up. Aberforth discovered their elaborate scheme to overthrow Muggles, and as a fight broke out, a stray curse killed Ariana. Aberforth claims Albus was glad to be rid of his encumbrance, but Harry says Dumbledore was never freed. After Albus drank the potion in the sea cave, Harry believes the raving Albus was pleading with Grindelwald not to hurt Aberforth and Ariana. Harry avers not to abandon Albus' mission. Surprisingly, Aberforth relents and shows the Trio a secret passage into Hogwarts. He later joins the battle inside the castle.
Prior to the big battle, the Trio, hidden inside the Shrieking Shack, overhears Voldemort discussing the Elder Wand with Snape. Voldemort suspects it performs poorly for him because Snape actually commands it, he being the one who murdered Dumbledore. Voldemort orders Nagini to kill Snape, then leaves. Before Snape dies, Harry captures his memories in a flask that then he empties into the Pensieve. Harry first sees Snape pleading with Dumbledore to protect Harry's mother, Lily, from Voldemort. Next, Snape is anguished over Lily Potter's death. Dumbledore says if Snape truly loved Lily, then he will protect her son when Voldemort returns. Snape grudgingly agrees but demands Dumbledore never tell anyone. In another next memory, Snape is railing about Harry being a bad student, while Dumbledore asks Snape to watch over Professor Quirrell. The scene shifts to Dumbledore and Snape at the Yule Ball. Snape says his and Igor Karkaroff's Dark Marks are growing more distinct; Dumbledore muses that perhaps students are sorted into their Houses too soon, apparently implying Snape might have been better suited to a different House than Slytherin.
While still in Snape's memories, Harry now sees a semi-conscious Dumbledore, his hand blackened after putting on Marvolo Gaunt's cursed ring. Snape treats him, but he can only slow the curse, not reverse it. Dumbledore has a year to live at most. The ring, now cracked, and the Sword of Gryffindor lie on Dumbledore's desk. Dumbledore says this makes things easier, and discusses Voldemort's plot to have Draco Malfoy murder him. Snape says Voldemort intends for Draco to fail, solely as a means to punish the Malfoys. Dumbledore guesses Voldemort intends that Snape will complete Draco's job, as Voldemort will no longer need a spy at Hogwarts once it falls under his control. Dumbledore demands Snape's promise to watch over the students, and asks that he kill him when the time comes, both to save Draco's soul, and allow Dumbledore to die with dignity. Snape, protesting, asks about his own soul, but Dumbledore responds that only Snape can determine if agreeing to his request will damage it. Snape, reluctantly, gives his word.
In Snape's next memory, Dumbledore is explaining to Snape that he was denied information given to Harry because Snape's mission puts him at a greater risk of being detected. Snape, still angry, threatens to rescind his earlier promise. Later, Dumbledore warns Snape that if Voldemort suddenly becomes protective towards Nagini, then Harry must be told that he is a seventh, accidental Horcrux; Voldemort must kill Harry before Voldemort can be killed. Snape is deeply dismayed that Dumbledore has only been protecting Harry so Voldemort can kill him. Dumbledore asks if Snape is starting to care about the boy. Snape, denying this, produces his Patronus, a doe, the same as Lily Potter's, who he still loves.
In Snape's next memory, he is talking to Dumbledore's portrait in the Headmaster's office. The portrait tells Snape he must give Voldemort the correct date for when Harry leaves Privet Drive, if he is to retain Voldemort's trust. Snape is to plant an idea into Mundungus Fletcher's mind to use multiple Harry decoys, disguised by Polyjuice Potion. In Snape's final memory with Dumbledore, Phineas Nigellus Black's portrait has just reported that Harry and Hermione are in the Forest of Dean; Dumbledore's portrait tells Snape to plant the Sword of Gryffindor there for them to find.
Harry knows Voldemort can only be defeated by allowing himself to be killed. After Harry enters Voldemort's camp in the Forbidden Forest, Voldemort fires the Killing Curse at him. Harry awakens to find himself in an otherworldly place resembling King's Cross Station. A hideously-flayed, infant-like creature is wailing on the floor. Dumbledore suddenly appears in full health, telling Harry that he (Harry) has not died. When Voldemort used Harry's blood to re-animate himself, he tethered his life to Harry's; Harry cannot die while Voldemort lives. Harry's willingly sacrificing himself now shields his allies from Voldemort. The killing curse Voldemort cast at Harry has destroyed Voldemort's own soul fragment that was clinging to Harry.
Dumbledore also explains he believes that Harry and Voldemort's wands, already sharing a common core, merged even closer when wielded in a duel between two wizards who not only shared blood, but also some of the soul. Harry was the stronger wizard because Voldemort feared death, while Harry was prepared to die. Harry's wand thus imbibed some power from Voldemort's, making it more powerful than any other wand Voldemort used.
Dumbledore asks Harry's forgiveness for withholding information about the Deathly Hallows. As a youth, he was obsessed with them - eager to escape death, and achieve fame and glory. His resentment at having to care for his family made it easy for Gellert Grindelwald to befriend him. They bonded over their search for the Hallows, but wanted them for different reasons. Dumbledore desired the Resurrection Stone to reunite his family, while Grindelwald would have used it to command an Inferi army. Grindelwald sought the Elder Wand to defeat the Wizarding realm. Neither were interested in the Invisibility Cloak, both being proficient in Disillusionment charms, though Dumbledore had considered it for concealing Ariana.
Their brief friendship ended when they quarreled over Dumbledore's family obligations. After Ariana was killed, Grindelwald fled to Europe, beginning his reign of terror. Dumbledore shamefully admits he delayed fighting Grindelwald. After defeating him, he won the Elder Wand, and Grindelwald was imprisoned in Nurmengard, where Voldemort eventually found him; Dumbledore says Grindelwald claimed he never possessed the Elder Wand, perhaps a remorseful last act to protect Dumbledore. Dumbledore identified the gem in the Peverell ring as the Resurrection Stone, another Hallow. He put the ring on, hoping to see his mother and sister again, but the curse protecting it destroyed his hand and shortened his life.
Dumbledore says he withheld information about the Hallows so Harry would avoid the same trap Dumbledore fell into. He wanted Harry to gradually discover their true nature. Death's true master, says Dumbledore, is the one who does not seek to run from it.
Finally, Dumbledore says Harry can choose to travel on to the "other side" or return to the living world and fight Voldemort. Harry chooses to return, but asks if their conversation has been real or only in his mind. Dumbledore responds that it is in his mind, but that does not make it less real.
After defeating Voldemort, Harry addresses Dumbledore's portrait, saying the Resurrection Stone has been left in the Forbidden Forest, and the Elder Wand will be secretly returned to Dumbledore's tomb, in the hope that its power dies with Harry. The Invisibility Cloak will be passed on to his children. Dumbledore indicates his approval.
In the epilogue, Harry has named his second son Albus Severus, after the two Hogwarts headmasters, Dumbledore and Snape.
Strengths.
Albus Dumbledore is among the greatest wizards who ever lived, though his gentle, eccentric nature belies his prodigious magical talents and superior intellect. Although he confined himself to a quiet teaching career at Hogwarts, he has long been considered a major player in the wizard world, heading many prestigious organizations, and is often consulted by the Ministry of Magic on magical matters. He is also an innovative thinker who freely gives his opinion, and has acted as a rallying point during difficult times, showing great leadership against both implacable foe and arrant stupidity. He is widely believed to be the only wizard Lord Voldemort has ever feared, and is singularly dedicated to defeating the Dark Lord, knowing he would eventually return, despite the Wizarding world's adamant insistence he was long dead. Dumbledore is among the few in the magical realm who has always openly spoken Voldemort's name, believing it is unable to harm anyone. Though he does not fear Voldemort's name, when addressing Voldemort directly, Dumbledore calls him "Tom," his birth name.
Perhaps unusually for a wizard, Dumbledore is also an inventor, specifically of mechanico-magical devices. His office contains many small, clockwork mechanisms performing unknown functions. We see two devices in action: a small object which, when queried, produces a smoke plume forming into the shape of the object or entity being asked about, and the Deluminator, which apart from storing light sources, also allows the owner to hear conversations about him, and can transport him to where that conversation is taking place. He bequeathed the latter object to Ron Weasley, who was later able to use it, though it appears the Ministry of Magic was unsuccessful in determining these devices' purposes when studying them.
Dumbledore is also generous and fair with those disenfranchised from the wizarding world, believing they deserve equal status. He employs Remus Lupin (a werewolf), Argus Filch, and Mrs. Figg (both squibs), and also Dobby and Winky (free elves no one else would hire). He also employed Rubeus Hagrid as Hogwarts grounds and game keeper after his expulsion from Hogwarts, believing he was innocent, and eventually promoted him to professor (Care of Magical Creatures).
Dumbledore tended to believe the best in most people. This is most evident when, after witnessing Severus Snape's deep remorse over his Death Eater past, permitted him to teach at Hogwarts, though this also allowed him to procure Snape's cooperation as a double agent in return. Many believe Dumbledore's bestowing so much trust in those with questionable pasts was misguided, though his nearly succumbing to Dark magic in his youth made him realize it is always possible to redeem oneself.
Family is also important to Dumbledore, and he deeply loved his deceased parents and sister. Although he failed his mother and sister, he recognized and accepted responsibility for how his actions contributed to their premature deaths, a fact that haunted him the rest of his life.
Weaknesses.
Albus Dumbledore's greatest weakness seems to have been a certain inevitability about his own failings. This is particularly marked in Book 6, but is foreshadowed throughout the series where he is always preparing Harry as the one who must vanquish Lord Voldemort.
A brilliant student, Dumbledore often used his academic pursuits to shield himself from family obligations, letting the burden for his impaired sister's care fall upon his mother, Kendra, and his younger brother, Aberforth. Dumbledore did put aside his personal pursuits to head the family after his mother's untimely death, but he bitterly resented taking on this responsibility and apparently did a poor job. This sense of martyrdom contributed to his forming a close, albeit short-lived, relationship with Gellert Grindelwald, a young Dark wizard. Albus was affected by Grindelwald's influence, and was briefly seduced by Dark magic's powerful allure, though he never actively pursued it. Unfortunately, his poor judgment regarding Grindelwald was a significant factor in his sister's tragic death, and forever haunted him. Despite following a light path ever after, Dumbledore never trusted himself around power, and instead spent his entire career at Hogwarts, an isolated place away from temptation. 
Dumbledore was prone to being aloof and secretive, and while this undoubtedly helped him surprise his enemies, it may also have prevented him from gathering more trusted confidants who could have acted as advisers. Though Dumbledore often consulted with the former Headmasters' portraits, their opinions on current events were restricted to their confined vantage point and often seemed outdated.
This proclivity for secrecy may have caused Dumbledore to withhold vital information from Harry when he probably should have been more forthcoming. His reticence particularly hampered Harry's mission to hunt Lord Voldemort's Horcruxes, a task that may have taken years and ultimately could fail. Dumbledore, who may have intended to share more with Harry before his death, knew he had only a short time left to live, so it is surprising that he gave Harry inadequate instruction for such a difficult and potentially fatal task. Though Dumbledore was rightly concerned that Harry's discovery about, and possible obsession with, the three Deathly Hallows could derail his pursuit for Horcruxes, it seems Harry's quest was made far more difficult and dangerous than necessary. It was also a gamble as to whether Harry would even discover the Hallows' existence or learn their significance.
Relationships with Other Characters.
Even though considered one of the most powerful wizards that lived, Albus Dumbledore apparently led a rather secretive, solitary, and bookish life. And while readers may initially assume his most significant relationship was the one he shared with Harry Potter, it is actually a few other key people who have mostly shaped his character, as well as guided his destiny, though not necessarily intentionally. Dumbledore is among the most complex, mysterious, and perplexing figures in the entire series.
At Hogwarts.
Dumbledore was surrounded by faithful Hogwarts staff and loyal Order of the Phoenix members. While he mostly assumes a leadership role, Dumbledore has strong relationships with several main characters other than Harry, including (but not limited to) Severus Snape and Minerva McGonagall. 
Dumbledore is on friendly terms with all the staff of Hogwarts, and takes a personal interest in how they are getting along. He seems to be aware of nearly everything that is happening in the school, including developing issues which he acts to defray before they become critical – for instance, he seems to know about Umbridge's plan to dismiss Professor Trelawney, and has arranged for a replacement even as Umbridge is trying to expel Trelawney from the school. However, with possibly a few exceptions, Dumbledore reveals very little of himself to the staff of Hogwarts.
Further discussion of Dumbledore's relationships with Hogwarts staff comprise something of a spoiler and so are in the Greater Picture section below.
The Dumbledore Family.
Like many other Hogwarts faculty, Dumbledore never married or had children. His only remaining immediate family was his brother, Aberforth, who also was unmarried and childless.
Little is known about Dumbledore's relationship with his family while he was growing up, though their history became marred with ongoing tragedy. His father died in Azkaban prison when Albus was still a boy. And though he loved his mother Kendra and sister Ariana, who was handicapped after she was attacked by Muggle boys, he distanced himself from Ariana's care whenever he was at home, leaving it to his mother and Aberforth. Albus was not only deeply affected by his mother's and sister's tragic premature deaths, but was forever guilt-ridden over how his actions contributed to their demises. This fueled his conflict with Aberforth, who had deeply resented Albus' shirking family responsibilities, then blamed him for Ariana's death, though his own hot temper was a factor in igniting the three-way duel between the two brothers and Gellert Grindelwald. This is likely the only thing that allowed them to maintain a respectful, though distant, truce later in life, both never wanting to know whose stray curse accidentally struck and killed their sister. 
Despite Aberforth's lingering resentment toward Albus following his death, he puts aside his personal feelings to help Harry Potter complete Dumbledore's mission to defeat Voldemort. And though Albus knew his own brilliance outshone that of his brother, he considered Aberforth's character stronger, wiser, and nobler than his own.
Harry Potter.
Dumbledore is Harry's kindly, though rather eccentric mentor during his Hogwarts' school years. Although Dumbledore and Harry grew close, probably closer than with any student under his tutelage, Dumbledore never became, nor did he attempt to be, a surrogate father to Harry. They primarily remained as student and mentor. Knowing that only Harry could defeat Voldemort, Dumbledore spent much time grooming him for his fateful encounter with the Dark Lord, though Dumbledore withheld crucial information, including that the only way to destroy the soul shard Harry unknowingly carried within him was to have the Dark Lord murder him. Dumbledore had always seemed rather pragmatic regarding Harry's fated demise, completely accepting that Harry must be sacrificed in order to save the Wizarding world from the Dark Lord. Dumbledore realized later, however, that by utilizing Harry's blood to resurrect his body, Voldemort unwittingly provided Harry the protection he needed to survive his own death at Voldemort's hand. 
Though Harry is magically powerful and had once survived Voldemort's killing curse, causing him to be dubbed "The Chosen One," many were still critical that Dumbledore entrusted an important secret mission to an as-yet unqualified wizard. Dumbledore may have actually agreed with them, but for reasons he alone understood, Harry was the only wizard who possessed the ability to defeat Voldemort. Even so, Dumbledore recognized Harry's weaknesses and his need to "go it alone", and strongly urged him to always seek Ron and Hermione's advice and help. 
Harry is devastated when Dumbledore is killed in book 6, though he soon came to doubt Dumbledore's true intentions and his mission to hunt Voldemort's Horcruxes after dark secrets in Dumbledore's past emerged. Harry's bitter disappointment in the late headmaster's failings initially prevented him from seeing that, unlike Gellert Grindelwald, Dumbledore's youthful foray into Dark magic was little more than a brief, youthful flirtation filled with idle theories and never-applied beliefs that he ultimately rejected. If anything, Dumbledore's shame over his lapsed judgment probably made him even more passionate in protecting others from Dark influences. As Dumbledore himself had once taught him, Harry finally comes to realize that it was Dumbledore's deliberate choices in life that made him the great man he truly became. Harry names his second-born son, Albus Severus, to honour both Dumbledore and Professor Severus Snape.
Tom Marvolo Riddle.
Dumbledore was closely tied to the Dark wizard Tom Marvolo Riddle (later known as Lord Voldemort) throughout his life. When he first met the eleven-year-old Tom Riddle in an orphanage, Dumbledore sensed this wizard was different, though he never suspected the young boy would become the most powerful Dark wizard in history. At Hogwarts, Dumbledore always kept a close eye on Riddle without revealing his suspicions to the other faculty, hoping Tom had abandoned his thievery and cruel ways. Though he was a brilliant student, Tom changed little, and instead crafted a false facade, charming his teachers while he quietly began sowing his evil empire, recruiting fellow Slytherins to become Death Eaters. Only Dumbledore suspected Tom was engaging in Dark activities while at Hogwarts, though he was unable to prove anything.
Riddle then returned after a decade away from Hogwarts to apply for a job; Dumbledore, now Headmaster, spoke with him. We see that Dumbledore mentioned how his former student had changed for the worse. Dumbledore received ongoing reports about Riddle's activities, so when Riddle applied for the Defence Against the Dark Arts teaching position at Hogwarts, Dumbledore knew about his new name, and mentioned his Death Eater associates. Dumbledore rightly suspected Riddle had an ulterior motive for wanting the job, and believed Riddle placed a curse on the position after being turned down. Ever since, every DA instructor lasted only one year.
Voldemort's biggest hurdle to conquering the Wizarding realm was always Dumbledore, even though Voldemort was supposedly the most powerful wizard in history. Dumbledore was always aware of Riddle's sinister nature and was never taken in by his superficial charm. It was also clear that Dumbledore understood his true nature better than anyone, and this insider knowledge helped Dumbledore prepare Harry for his predestined encounter with Voldemort. 
Voldemort later devised a scheme for Draco Malfoy to murder Dumbledore, though his real intent was to kill Draco when he failed, solely as a means to punish his father, Lucius Malfoy. Unknown to Voldemort, Dumbledore uncovered the plot, and used it to aid his own plan to defeat the Dark Lord.
We note that Voldemort, later, wanted to capture the Elder Wand, the most powerful wand in the world, once he learned of its existence; although this is not stated directly, it is likely that once he learned Dumbledore wielded that wand, Voldemort assumed that it was the wand alone that had given Dumbledore the power to defeat him. Although Voldemort physically possessed Dumbledore's wand following his death, he was never its true master. Even if he had captured it directly from Dumbledore, it is questionable if it would have performed well for him. The author has stated on her website that only those able to face death fearlessly can truly control a wand containing a Thestral hair, as the Elder Wand did. 
Gellert Grindelwald.
Though short-lived, Dumbledore's relationship with Gellert Grindelwald was probably his most significant in that it forever altered his adult life. Bitter over delaying his professional goals to instead care for his family after their mother's untimely death, Dumbledore became enthralled with Grindelwald, a young wizard who came to live in Godric's Hollow after being expelled from Durmstrang. Grindelwald was as brilliant as Dumbledore, but readily practiced Dark magic. Dumbledore, feeling he had found a soul mate, came to share Grindelwald's idea to conquer and rule Muggles, though they differed on how to execute this. Dumbledore favored a benevolent approach, convincing himself it was for "the greater good" of all, while Grindelwald espoused a more sinister method. 
It seems inconceivable that the Dumbledore we know could ever endorse such a wicked scheme. However, his tragic youth, misguided ambition, and blind attraction to Grindelwald apparently rendered him susceptible to Grindewald's charismatic, but evil allure. It was only after Aberforth, Dumbledore's younger brother, uncovered their plot, resulting in a three-way duel ending with their sister's accidental death and Grindelwald's abrupt departure, that Albus recognized his own serious failings. But even after Grindelwald began his rampage in Europe, Dumbledore waited over five years to respond to the Wizarding world's pleas for his help. Lingering feelings for Grindelwald may have prevented Dumbledore's confronting and defeating his former friend sooner than he did. Whether his delay caused more innocent deaths or if that affected him is unknown, but forever after, Dumbledore dedicated himself to fighting Dark forces and protecting Muggles' rights. 
Analysis.
Throughout the Harry Potter series, Dumbledore has acted as a trusted mentor to Harry, and, in this way, has contributed greatly in Harry's victories over Voldemort.
During the series, Dumbledore's character changes considerably, and no single analysis can do him justice. It seems reasonable to analyze Dumbledore's character as more information is revealed about him in each successive book.
The First Five Books.
Dumbledore's character in the series' first five books seems largely consistent. He appears as the slightly dotty, elder genius, whose occasional strange decisions are honoured because he is respected for his extreme intelligence and vast knowledge. His offbeat behavior is often considered utterly harmless, and his wisdom is sometimes interpreted as eccentricity. And his more controversial decisions – hiring Remus Lupin, trusting Severus Snape – are accepted purely because he has long been revered for his genius. His strength of character is particularly tested in "Harry Potter and the Order of the Phoenix", when his reputation is publicly attacked because he repeatedly reports an unpopular fact, namely that Lord Voldemort has returned.
Dumbledore cares about Harry, more so than any other student at the school. He gently, or sometimes not so gently, educates Harry as to his place in the Wizarding world, and attempts to train Harry for the role that a prophecy has fated him for: Harry is the Chosen One–he must stand against Voldemort. At the end of the fifth book, in Dumbledore's office, Harry's importance to Voldemort is revealed, and we learn why Dumbledore has been so keenly interested in and attentive to Harry.
Half-Blood Prince.
On many fan sites, it was remarked after "Harry Potter and the Half-Blood Prince's" publication that Dumbledore was acting out of character. In retrospect, we can see that he has indeed changed; however, there is a legitimate reason. When he re-enters the story, his hand is already injured, indicating that he knows he has only one year, at most, left to live. As such, he can no longer wait; whatever he must accomplish now has a definite deadline. On several occasions, he comments on not fearing death, and this may seem a contradiction. However, his actions are motivated not out of a fear of death, but rather from an urgency to complete the necessary work, including imparting a certain amount of knowledge to Harry, before his time ends.
Dumbledore, knowing only Harry must stand against Voldemort, directs much energy to teaching Harry what he knows about Voldemort to enable Harry to defeat the Dark Lord. He continues uncovering information about Voldemort's past that will assist Harry. Guessing that multiple Horcruxes exist, Dumbledore carries out research that leads him to the ring Horcrux and to the original Locket Horcrux's resting place.
It is interesting to note that Dumbledore values Harry more highly than himself in the cavern where the locket Horcrux was hidden. Likely this is due to the prophecy, but Harry has yet to recognize this.
Many people believed, by this book's end, that Dumbledore had erred badly in placing his faith in Snape. Whether or not that had been a mistake remains unknown until the final book.
Deathly Hallows.
In the series' final book, we are finally granted glimpses into the true depth of Dumbledore's character. Elphias Doge's eulogy reminds Harry that he knew almost nothing about Dumbledore's past, having seen him only as the kindly Headmaster who was his protector and mentor. Harry never thought to ask Dumbledore about his earlier life, perhaps youthfully assuming that he sprang from the earth, fully grown with long silver hair and beard. It is only after Rita Skeeter's muck-raking biography about Dumbledore suggests there was something unsavoury about Dumbledore's background that Harry sees Dumbledore somewhat differently. But finally it is Aberforth Dumbledore, recounting the family story to Harry, that reveals Dumbledore as a schemer who mostly kept his own council, and brings us to the realization that Dumbledore had been manipulating Harry as a pawn to act directly against Voldemort. In King's Cross, Dumbledore tells Harry that as a youth, power proved too alluring for him to resist, causing him to carefully avoid it in his adult life. However, it seems he was less averse to being the power behind the throne, driving Fudge, Harry, and others in directions he felt they needed to go.
Revelations in this book also show us how Dumbledore was preparing Snape over the length of the series for his role in supporting Harry and thwarting Voldemort. Snape's actions throughout the series only become fully clear with the revelations in this book about his interactions with Dumbledore.
Albus Dumbledore's Age.
Dumbledore's age and accomplishments are frequently discussed on the various fan sites. Dumbledore is about 115-years-old when he dies, and the author has given his birth year as 1881. His Wizard card states that he is noted for his work in Alchemy with Nicolas Flamel. In passing, we should mention that there is a Nicolas Flamel in Muggle literature as well; he was a relatively famous alchemist in the 1300s. The fictional Nicolas Flamel and the real one apparently have similar, but not identical birth dates. The book in which Hermione uncovers information about Flamel is extremely old, and yet it gives ages for Nicolas and his wife Perenelle. Unless the book magically updates ages, the ages in the book must be outdated by several years. Therefore, Flamel in the Wizarding world is at least 665 years old (the age apparently given in the book), potentially as much as 750 years old if the book is only a hundred years old. If Dumbledore is a mere spring chicken of 115, and Flamel was at least 500-years old when Dumbledore was born, then how could Dumbledore have helped Flamel make the Philosopher's Stone upon which his ongoing life had depended? Careful reading reveals, however, that while Dumbledore worked with Flamel in alchemy, it is never stated he helped him create the Stone. 
There is insufficient information about wizards' typical lifespans, but Dumbledore, when he is around 110 years, is described as appearing old, and he appears more aged than most other characters in the books. Only Nicolas Flamel is explicitly described as being older at 665 years old, though Elphias Doge attended school with Dumbledore and should be the same approximate age. Also, Bathilda Bagshot saw Dumbledore's mother Kendra as a contemporary and thus was likely older than Dumbledore. In addition, Griselda Marchbanks said she "Examined him personally in Transfiguration and Charms when he did N.E.W.T.s...", which means she had at least graduated from Hogwarts at the time. Professor Tofty is mentioned to look like "the very oldest and baldest examiner", which means he could possibly be even older than Professor Marchbanks. Flamel ultimately died after surrendering the Philosophers Stone (also known as the Sorcerer's Stone), which preserved his life, to prevent it falling into Voldemort's possession. Flamel shared the Stone with Dumbledore, but it is unknown to what extent, if any, it may have been responsible for extending Dumbledore's life.
Greater Picture.
Relationships at Hogwarts.
As mentioned, Dumbledore has strong relationships with Severus Snape and Minerva McGonagall. 
To readers, in the first six books McGonagall appears to be Dumbledore's closest confidant and advisor, and headed Hogwarts whenever Dumbledore was absent. She was steadfastly loyal to him, and though she is strong-willed and opinionated, she always abided by his decisions. It is only in the last book that we learn Snape was closer to Dumbledore than anyone, though their relationship was not without occasional rancor and disagreements. Snape was under a huge obligation to Dumbledore, who granted him a safe sanctuary after his defection from Voldemort. Dumbledore, disdainful over Snape's past deeds as a Death Eater, demanded much in return, forcing Snape to act as a double agent against Voldemort and his minions. Snape also became one of Harry Potter's protectors and later secretly aided his mission after Dumbledore's death, despite Snape's intense dislike for the boy. 
Snape was obligated to Dumbledore for the remainder of his life, and despite Harry's doubts and misgivings, Snape's loyalty to Dumbledore never wavered and was always freely given. In return, Dumbledore entrusted Snape with knowledge no one else was privy to, not even McGonagall. He certainly never trusted McGonagall any less, and he valued her abilities, but he was able to exploit Snape's Death Eater past by having him infiltrate himself back into Voldemort's inner circle. And Snape, being highly skilled in Occlumency, could safeguard Dumbledore's secrets, particularly those regarding Harry Potter, far better than McGonagall. Dumbledore's own brief seduction by Dark magic in his youth may have made him more sympathetic and forgiving of Snape, creating a unique bond between two men with similarly tainted pasts.
The Ending of "Half-Blood Prince".
Dumbledore's murder by Snape created much speculation and controversy in the fan community. Perhaps it was wishful thinking, a belief that Dumbledore was too powerful, too clever, or that his part was not yet played out, or even the clues dropped either deliberately or accidentally by the author, but until the seventh book's release, many readers were convinced, or at least hopeful, that Dumbledore was not truly dead, and had instead arranged with Snape to fake his death, and that he would somehow return to support Harry through the seventh book.
While there were many clues suggesting Dumbledore's demise was something else entirely, the author stated numerous times that Dumbledore definitely died in the sixth book. This did not mean that Dumbledore would have no further influence beyond his death. The author has admitted that she had trouble writing some of his scenes in "Harry Potter and the Deathly Hallows" (The Observer, 6 February 2007). As his portrait immediately appeared in the Headmaster's office, it could be speculated that he would likely play a part in "Harry Potter and the Deathly Hallows". An interesting point that has come up is linked to another statement Dumbledore made in "Harry Potter and the Chamber of Secrets", where Dumbledore says, "I will only "truly" have left the school when none here are loyal to me." Harry echoes this statement at the end of "Harry Potter and the Half-Blood Prince", in a context which leads us to believe he is truly loyal to Dumbledore. We know that it was that loyalty that summoned Fawkes to Harry in the Chamber of Secrets. Will it perhaps have the same effect again in the final book?
One interesting theory surfaced about Dumbledore's death at Snape's hands. Going back to Harry's first Potions class, back in "Harry Potter and the Philosopher's Stone", Snape says: "I can teach you how to bottle fame, brew glory, even "stopper death"..." (We note that in the Scholastic edition, Snape's speech ends "and even put a stopper to death...") This scene is apparently very important as readers are referred back to it time and time again.
Now, let us look at the effect of the cursed necklace on Katie Bell in "Harry Potter and the Half-Blood Prince". Quoting Professor Dumbledore: "She appears to have brushed the necklace with the smallest possible amount of skin: there was a tiny hole in her glove. ... Luckily, Professor Snape was able to do enough to prevent a rapid spread of the curse—" So we have the information that the type of curse that was on the necklace spreads from its contact point, and that Snape can stop its spread.
From elsewhere in that book, there is information that it was Snape whom Dumbledore sought after injuring his hand. Was the ring, which contained the Horcrux, or some part of its surroundings, similarly cursed? It is possible, given that Dumbledore would have felt duty-bound to destroy the Horcrux before seeking assistance, that the curse was irreversible by the time he reached Snape. The only thing that may be keeping Dumbledore alive at this point is the potion that "stoppers death" (or "puts a stopper to death"). This would explain Dumbledore's different behaviour in this book; he knows his time is limited, and he is in a great hurry to pass on all he knows before his inevitable departure. 
Snape knew that he was not murdering Dumbledore because Dumbledore was effectively already dead, kept alive only by a potion that Snape administered, and which would not be effective for much longer. There may have been other arrangements between them, and it may have been Dumbledore's plan for Snape to kill him to solidify Snape's position in Voldemort's hierarchy. It is important to note that Dumbledore did not fear death; we see this on several occasions, most notably at the end of the first book, where Dumbledore says, "after all, to the well-organized mind, death is but the next great adventure." This also tallies with Snape's expression of extreme distaste as he cast the Killing Curse at Dumbledore – was this an act he had to perform, rather than one he wanted to? It also dovetails with Snape's actions as he flees Hogwarts. Anticipating Harry's every move and blocking his curses, he could easily have injured, Stunned, or even killed him. Instead, he does nothing to harm Harry, and practically uses the confrontation to tutor him on defensive strategy. Also, it should be noted that when Dumbledore says, "Severus... Please..." (page 595 US/556 UK), he is actually pleading for Severus to end his life. It is revealed in the final book that Dumbledore forced Severus to agree to doing this, and that Severus later expressed great reluctance to carry out this promise.
Gellert Grindelwald.
Throughout the seventh book, it is gradually revealed that when Dumbledore was seventeen, he and the Dark wizard Gellert Grindelwald became close friends. We can see, though the young Dumbledore could not, that the evil Grindelwald was power-hungry, and his overall intent was to conquer. Dumbledore's ultimate aim was to make it safe for those like his sister Ariana to exist. Muggles would live under Wizard-kind's benevolent rule, making it possible for wizard offspring and Muggle children to co-exist harmoniously. One simple personality test is selecting a specific Hallow believed to be the most valuable, and why. Grindelwald clearly thought the Elder Wand, unbeatable in a duel, was the most desirable, with the Resurrection Stone running second. Albus felt the Resurrection Stone was more important. To Grindelwald, the Resurrection Stone meant commanding an Inferi army; to Albus, it was his parents returned to him, thereby lifting his burden for his siblings' care. Why did Dumbledore fail to see that Grindelwald was choosing a path leading to corrupt power and domination? The author has said that Dumbledore was infatuated with Grindelwald, and that being in love had blinded him. He overlooked Grindelwald's faults, and with youthful foolishness, perhaps thought he could change Grindelwald to his own, somewhat more gentle ends. According to Rowling, Dumbledore falling in love with a Dark and selfish person like Grindelwald, and the later consequences, is his biggest tragedy. As a result, Dumbledore never again trusted himself with power, causing him to decline the Minister for Magic post, among other prominent positions, and instead confine his career path to Hogwarts where he would be less tempted.