Miles O'Brien
Senior Chief Petty Officer Miles Edward O'Brien was a 24th century Human Starfleet non-commissioned officer who, following his service during the Federation-Cardassian War, served as transporter chief on board the  for several years before being promoted to chief of operations aboard starbase Deep Space 9. After the Dominion War he accepted a professorship at Starfleet Academy on Earth.

Early life 
Miles O'Brien was born in Ireland, Earth, in September 2328. ()

O'Brien claimed he could trace his ancestry back to the 11th century Irish king Brian Boru (whom he occasionally played in a holosuite program). Another notable O'Brien ancestor was Sean Aloysius O'Brien. ()

O'Brien was proud of the fact that he was raised on real food as his mother believed that replicated food was less nutritious. When preparing meals for her family, his mother would handle and cook meat. ()

O'Brien had two brothers. His mother passed away in 2368 and his father, Michael, remarried a year later, though Miles never met his new stepmother. () His relationship with his father had been a somewhat rocky one during Miles' adolescence; Michael had pushed Miles to pursue his music career, making him practice the cello at least once a day, and was somewhat upset by his son's enlistment in Starfleet. When Miles was seventeen years old, his father sent a recording of his work to the Aldeberan Music Academy. O'Brien declined the offer of admission to the Music Academy and enrolled in Starfleet – against his father's wishes. The two later reconciled their differences and O'Brien's father was eventually extremely proud of his son and his accomplishments. ()

As a child, O'Brien had a morbid fear of spiders. Following a mission on Zayra IV where O'Brien was forced to make a critical repair in a Jefferies tube containing Talarian hook spiders, he found that his fear had lessened, and he later kept a Lycosa tarantula, named , as a pet aboard the Enterprise-D. ()

Starfleet career 
In 2345, at the age of 17, O'Brien joined Starfleet as an enlisted crewman, where he attended Engineering School. () 

As of stardate 49648, O'Brien had served aboard a half dozen starships, participated in 235 separate combat engagements, and been decorated by Starfleet on fifteen occasions. Because of his impressive military record, O'Brien was recognized by a Starfleet formal inquiry as an expert in starship combat. ()

O'Brien's career was so well respected that Captain Keogh of the  considered the chief's experiences an asset before launching a rescue mission for Commander Benjamin Sisko in the Gamma Quadrant in 2370. ()

The USS Rutledge 

One of his first assignments was aboard the  under the command of Benjamin Maxwell, where he served as junior tactical officer during the Cardassian War. A year later, O'Brien was present at the aftermath of the Setlik III massacre, where his technical skill was useful in repairing a field transporter, allowing him and thirteen other Starfleet personnel to escape a Cardassian patrol. This earned him a promotion to primary tactical officer. O'Brien also served as part of a squad to aid the survivors of the massacre, as Cardassians were still patrolling the settlement; he helped a group of women and children but was ambushed by two Cardassians. He was able to incapacitate one of them, but in fighting with the other one he accidentally killed his assailant when a phaser passed to him was set to maximum. Until then, O'Brien had never killed anything or anyone (he was even worried about swatting mosquitoes as a child) and the incident left him with a deep-seated resentment towards Cardassians, bordering on outright racism on occasion. He often referred to them by the derogatory term "Cardies". () Many years later, he remarked to Glinn Daro that it was not Cardassians that he hated, but rather the person he became because of them. ()

O'Brien was even styled "the hero of Setlik III" due to his actions in an engagement with Cardassian forces on that planet, a title he seemed to tolerate rather than enjoy. During a salvage mission to Empok Nor, Elim Garak challenged O'Brien to a game of Kotra, saying he would love to play against the "Hero of Setlik III." ()

The USS Enterprise-D 
O'Brien transferred to the USS Enterprise-D in 2364 with the rank of chief petty officer, under the command of Captain Jean-Luc Picard. During the Farpoint Mission, he was assigned as relief flight control officer. He also stood duty in the security department, but was most often seen working as transporter chief, where he was involved in, among other events, the rescue of Captain Picard from the Borg in 2367. (; )

In 2367, Miles was forced to confront his former commanding officer when Captain Maxwell went rogue, launching attacks on Cardassian outposts and ships in spite of a peace treaty between the Federation and Cardassia. O'Brien's knowledge of transporter systems allowed him to beam aboard Maxwell's ship, the , while her shields were up, giving him a chance to reason with Maxwell, ultimately preventing further bloodshed. ()

During the Klingon Civil War, O'Brien also made use of his training as a tactical officer following Lieutenant Worf's resignation from Starfleet. As a result, he was heavily involved in the deployment and maintenance of the tachyon detection grid that ultimately decided the conflict. ()

In 2368, a quantum filament caused major damage to the Enterprise. Unable to communicate with the rest of the crew, O'Brien, together with Lieutenant Commander Deanna Troi, Ensigns Ro Laren and , was trapped on the bridge, while his heavily-pregnant wife Keiko was stuck in Ten Forward. The quantum resonance of the filament caused a polarity shift in the ship's antimatter containment fields, leading to a progressive degeneration in the fields, threatening the ship. Ro suggested a saucer separation to save the primary hull, while sacrificing the stardrive section. O'Brien strongly opposed this plan and stated that it would be a "pretty cold-blooded thing to do." Eventually, thanks to his prowess in keeping the containment field stable long enough, Troi rejected Ro's proposal, and the antimatter containment was fully restored by Commander Riker and Lt. Commander Data shortly before Keiko delivered her baby in Ten Forward. ()

Later that year, O'Brien, along with Troi and Data, was taken over by an alien lifeform which forced them to take hostages to use as a bargaining chip in negotiating with Picard. Among the prisoners were Molly and Keiko O'Brien. Eventually, the lifeform left when it was discovered that the moon was actually a penal colony and that this was an attempt for the lifeform to escape. ()

Deep Space 9 

By 2369, O'Brien had been serving in Starfleet for 22 years. In that year, O'Brien left the Enterprise, transferring to Deep Space 9 with a promotion, and was assigned the role of chief of operations. His primary task during the early days of his posting was to repair the damage done during the withdrawal of the Cardassians from the station. He was instrumental in moving the station from its orbit of Bajor out to the Denorios belt, following the discovery of the Bajoran wormhole. ()

On Deep Space 9, O'Brien had a half dozen new problems every day to fix as the station's combination of Cardassian, Bajoran and Federation technologies weren't meant to work together and would constantly break down. But he much preferred his busy schedule on the station; finding it easier to when he was serving aboard the Enterprise where he would get bored spending most of his time waiting around the transporter room for something to break down and that the station needed him. ()

Not long after his arrival, O'Brien received a note on his record for violating the Prime Directive, after assisting in the escape of a Tosk, one of the first contacts from the Gamma Quadrant, disobeying direct orders from Commander Sisko. Tosk was a being raised to be the prey in a hunt by those known as the Hunters. ()

He later found himself entangled in local Bajoran politics and folklore when visiting a remote village on the planet. Following the death of the local , O'Brien was thrust into the role, forcing him to try and maintain the unity and strength of the inhabitants against a Dal'Rok. ()

In 2369, O'Brien's assistant Neela attempted to assassinate Vedek Bareil. O'Brien discovered the plot and informed Sisko just in time to save Bareil's life. ()

He assisted Kira Nerys in rescuing Li Nalas from the Hutet labor camp, and defended the station against the Circle, a Bajoran terrorist group who wanted the Federation to leave the sector. ()

In 2370, O'Brien was assisting the T'Lani and Kellerun militaries in disarming and neutralizing their harvester weapons when a sabotage attempt exposed him to deadly nanobiogenic gel. In the resultant escape and rescue, he almost succumbed to his injuries, but was saved by Julian Bashir, an act which developed their friendship (see Personal, below). Several months later, while assisting in preparations for a Parada peace conference on Parada II, O'Brien was kidnapped and replaced with a replicant, created to disrupt the conference. The duplicate O'Brien later died after others became aware of the threat he posed, and the real O'Brien was recovered by DS9 personnel. ()

Later that year, Quark tried to use Bashir and O'Brien in a racquetball scam. He had fixed the game in O'Brien's favor and with everyone betting on Bashir, intended to clean up. ()

O'Brien became stranded with Sisko on an Earth colony, where an energy dampening field made it impossible to communicate with the orbiting runabout to leave the planet. O'Brien found out that it was an artificial field and was able to turn it off. ()

Sometime around stardate 47944, O'Brien was arrested by Cardassian forces and put on trial for allegedly supplying weapons to the Maquis, based on, among other evidence, a falsified voiceprint. He was sentenced to execution. The charges were later discovered to be part of a conspiracy by the Cardassians to discredit the Federation and give the Cardassian Union a stronger position from which to negotiate, and O'Brien was released. ()

In 2371, O'Brien helped disable a self-destruct mechanism on the station left by the Cardassians. He helped rescue Sisko from the past, and also worked with a group of female Cardassians on a science project on the station. One of the scientists wanted to become romantically involved with him, but he refused. () 

When the Klingons attacked and invaded Deep Space 9 in early 2372, O'Brien defended Ops against boarding parties, suffering minor injuries in the attack. At the time of the attack, O'Brien had been completing the retrofit of the station's weapons arrays. ()

His image was accidentally used in a holo-program by Julian Bashir and Garak when a runabout he was on was destroyed by Cardassian terrorists. The computer, under direction of Michael Eddington, stored his physical image in the open holosuite program (as the evil assassin Falcon) while his conscious mind was stored in DS9's computer core. ()

Later that year, O'Brien had been falsely accused of espionage, and was given the simulated memory of a twenty-year prison sentence following a visit to the planet Argratha. Upon returning to the station, O'Brien became paranoid and emotionally distressed which caused angry outbursts. He even began experiencing hallucinations of his cellmate Ee'char. Miles was temporarily relieved of his duties by Captain Sisko, on the recommendation of Doctor Bashir. As O'Brien's condition deteriorated, he attempted suicide, but was stopped by Bashir. ()

In late 2372, O'Brien commented that his career had included service on half a dozen ships. Even though none of those vessels had cloaking devices, O'Brien eventually became so used to the  being cloaked that he felt vulnerable aboard uncloaked ships.

He took part in the joint effort between the Federation and Jem'Hadar to track down a group of renegade Jem'Hadar soldiers that captured an Iconian gateway. ()

In 2373, O'Brien took part in an infiltration mission to the fortified Klingon moon of Ty'Gokor in an attempt to expose Gowron as a Changeling. For the mission, Miles had to be surgically altered to appear Klingon. ()

O'Brien, as part of a Defiant away team, discovered a crashed Jem'Hadar ship on a planet. When a Vorta and a team of Jem'Hadar came to retrieve the ship, a fight broke out. A crewman O'Brien had become close to, Enrique Muniz, also died as a result of wounds he received in battle, and this affected O'Brien deeply. ()

While away on Bajor, Keiko became possessed by a Pah-wraith. It threatened to kill Keiko unless O'Brien helped it to blow up the wormhole. He tricked it on the way to the wormhole and used the very energy beam it intended to kill the Prophets with to kill it instead, saving Keiko. He also went back in time to the original  and met Captain Kirk, helping to stop a Klingon named Arne Darvin from assassinating Kirk and changing history. ()

On an assignment to Empok Nor to get a part necessary for the station, he and his team found two Cardassians in stasis. Upon waking, they murdered some of the team before Garak killed one of them. Garak became infected with a drug in the Cardassians' systems and turned into an insane murderer, killing the other soldier and one of O'Brien's crew before O'Brien was able to disable him and return him to the station for treatment. ()

Service during the Dominion War 
O'Brien was partly responsible, along with Rom and Jadzia Dax, for creating and deploying the self-replicating minefield that blocked Dominion ships from entering the Alpha Quadrant, an event which precipitated the Dominion War. Miles abandoned the station with the rest of the station's Starfleet complement, taking station aboard the Defiant, where he remained for the first three months of the war. ()

Along with the rest of the DS9 command crew, O'Brien was pulled from front-line duty to take a captured Jem'Hadar vessel behind enemy lines. Despite his love of field rations, O'Brien bemoaned the lack of a replicator aboard the commandeered vessel. When the vessel crash-landed shortly after achieving its objective, O'Brien tore his uniform, much to his chagrin and the amusement of his colleagues. ()

He was part of the away team that confronted the Jem'Hadar on a planet after both sides crashed. The Jem'Hadar were betrayed by their Vorta and led into an ambush. The Vorta was about to run out of ketracel-white and feared the Jem'Hadar would kill him. ()

Following their rescue by the Rotarran, Miles took part in Operation Return, which successfully recaptured the station. He resumed his duties aboard the newly-retaken Deep Space 9. Shortly thereafter, he played a ceremonial role in the wedding of Jadzia Dax and Worf. ()

When the Defiant was captured by Jem'Hadar forces during a scientific mission, O'Brien was able to help Ensign Nog gain control of the ship from engineering by re-routing the bridge access codes. ()

In mid-2374, O'Brien was recruited by Starfleet Intelligence to infiltrate the Orion Syndicate arm on Farius Prime. During the mission, Miles grew friendly with Liam Bilby, a Syndicate operative. After Bilby was killed attempting to assassinate the Klingon ambassador, O'Brien took in his cat, Chester, as a family pet, and paid money into an account for his wife. ()

In late 2374, Molly fell into a time portal placing her three hundred years in the past. Upon being rescued, she was a teenager who had lived her life in a prehistoric era. She was unable to cope, and when returned into the portal found herself as an eight year old, where she helped guide herself back to her parents. ()

Following the death of Jadzia Dax in late 2374, O'Brien took part in the Rotarrans successful assault on the Monac shipyard, a mission intended by Worf to get his wife into Sto-vo-kor. ()

Later in 2375, Miles disappeared on New Sydney while attempting to track down Morica Bilby, Liam's wife, who had disappeared from her home on the planet. O'Brien's mission was unauthorized, and he received a reprimand as a result. ()

Shortly before the final battle of the war, O'Brien took part in the attempt to restore Vic Fontaine's casino. It had been taken over by Chicago gangsters. ()

Shortly before the end of the war, O'Brien accepted a position at Starfleet Academy as a professor of engineering. Following the Battle of Cardassia, O'Brien departed Deep Space 9 for Earth, to take up this new role. Immediately prior to leaving, he was still considering where exactly his family would settle on Earth. His crewmates all gave suggestions: Worf was particularly insistent he look at Minsk. ()

Legacy 

In the far future, O'Brien was remembered as a notable Starfleet officer, alongside Bradward Boimler. An educator instructing a classroom of children remarked that "[He was] perhaps the most important person in Starfleet history" and displayed to the class a holographic statue depicting O'Brien standing at a transporter console. ()

Personal relationships

Family

He married Keiko Ishikawa aboard the Enterprise on October 24th, 2367, and the couple had their first child, Molly, the following year. () Both joined O'Brien aboard DS9, albeit reluctantly on Keiko's part, where their second child, Kirayoshi, was born in 2373. O'Brien had a difficult time dealing with this pregnancy, mainly as a result of the baby's forced 'relocation' to Kira Nerys in late 2372, which saw the two struggling with a mutual attraction – one which both agreed to put aside. ()

As a ritual before going into battle, O'Brien recorded a "goodbye" message for his family in the event of his death. Each time he did so, he believed it would be the one they would hear. Between 2367 and 2372, he had recorded a total of eleven messages. () He also regularly wrote "sexy letters" to Keiko. ()

O'Brien described marriage as "the greatest adventure of them all. It's filled with pitfalls and setbacks and mistakes, but it's a journey worth taking because you take it together". ()

Friends 
Although an enlisted crewman with little official standing in his posts, O'Brien has regularly shown a talent for connecting with his commanding officers; Captain Benjamin Maxwell once described O'Brien as the finest tactical officer he ever had, and Captain Picard noted that Transporter Room Three – O'Brien's favorite room – wouldn't be the same without him. O'Brien generally reciprocated this respect, noting once in a conversation with Picard when discussing his past service with Captain Maxwell that he considered himself fortunate to have served under Starfleet's two finest captains, and later demonstrating the same respect to his new commanding officer, Benjamin Sisko. (; )

Julian Bashir 

Aboard Deep Space 9, O'Brien forged a strong friendship with Julian Bashir, the station's chief medical officer. Even though Dr. Bashir did take a liking in O'Brien, that sentiment was not reciprocated at first as Miles considered him arrogant and too talkative. He was also not looking forward to calling him by his first name as he had asked him to. Mutual respect developed when the two had to work together to survive on T'Lani III. When the two thought they were about to be killed, O'Brien admitted it was an honor to serve under the doctor. ()

A friendly rivalry developed between the two in racquetball, darts, and other activities. The two were frequent users of the station's holosuites, usually for historical reenactments of events such as the Battle of Britain and the Battle of Clontarf, and even created their own programs, including an accurate depiction of the Alamo. ( et al.)

Their friendship grew so close that O'Brien considered Bashir as important to him as his wife. While drinking and trying to cheer up Bashir about not being noticed by his Academy rival, Elizabeth Lense, O'Brien came close to admitting that he loved Bashir. On another occasion, O'Brien inadvertently expressed the wish that Keiko was more like Bashir. O'Brien was eventually able to accept that he could be close to both his friend and his wife. ()

O'Brien also thought very highly of Bashir. While he was talking about how much he loved his children, O'Brien even told Bashir that he thought Julian would make a great father. Doctor Bashir jokingly admitted that he wasn't the family type. () 

The friendship was strained at times. When Bashir and O'Brien were trapped on a planet with some rogue Jem'Hadar, Bashir decided to help their leader Goran'Agar find out why he was no longer addicted to the white. O'Brien was vehemently against such a proposal, noting that the Jem'Hadar were enemies of the Federation, and that freeing them of the white would make them a larger threat to the Alpha Quadrant. He was further resentful when Bashir ordered him to help. On another occasion, Bashir and a group of genetically-engineered Humans predicted that the Federation was doomed to lose the Dominion War. Miles was angry at the sheer arrogance shown by the group, noting that they were not as smart as they thought they were. ()

The friendship helped the two through troubled times. When O'Brien was given twenty years of prison memories for a crime he did not commit by the Argrathi and could not adjust, he attempted to kill himself. One of the false memories was that he had killed his best friend in prison, even admitting that had it been Bashir in the cell with him, he would have killed the doctor as well. It was Bashir who was able to talk him out of the attempt and get him help. () Later, as Bashir became desperate to find a cure for Odo's morphogenic virus, O'Brien came up with the scheme to lure a Section 31 operative onto the station, capture him, and then probe his mind for knowledge of the cure. Then, when Bashir decided to delve into Luther Sloan's dying mind for the knowledge, O'Brien insisted on going with him, which proved critical in keeping Bashir focused on obtaining the cure even when faced with the possibility of acquiring information that could allow him to shut down Section 31. ()

Worf 

Miles O'Brien and Worf knew each other from their early days on the Enterprise, although their relationship was that of a noncom and his superior. The two would play together in the crew's poker games. O'Brien participated in Wesley Crusher's Age of Ascension recreation for Worf, where he commented on the power of the Klingon painstiks. ()

O'Brien was the first person, besides Worf, to greet the Klingon's adoptive Human parents, upon their arrival on board the Enterprise, Worf's adopted father noting that he had served in O'Brien's position during his own Starfleet career. ()

Although Worf had to man the bridge at O'Brien's wedding to Keiko, he gave O'Brien a Klingon weapon as a wedding gift. In 2368, when the Enterprise was damaged by a quantum filament, Worf was forced to deliver Keiko's baby daughter, Molly, something apparently found quite stressful. He humorously noted that Molly resembled Miles. ()

The friendship strengthened when Worf transferred to Deep Space 9 in 2372. O'Brien was the first person to greet Worf when he arrived. Later, he introduced Worf to the game of darts, describing it as "poker, but with pointed tips." When Worf accepted the position of strategic operations officer (with a change of uniform from yellow to red), O'Brien commented how good Worf looked in red. ()

When the Defiant was damaged by the Jem'Hadar during their Karemma negotiations, and Worf found commanding the engineering team difficult, O'Brien helped Worf take a different approach to command. ()

When Worf discovered that the O'Briens were having another child, he altered his holiday plans to coincide with the birth, just so there would be no chance that he would have to deliver the baby (as he did with Molly). ()

During Worf's trial that demanded his extradition to the Klingon Empire, O'Brien described Worf as "an honorable man". In turn, Worf described O'Brien as an "outstanding officer" and a friend, relaying their mutual respect out loud. ()

Worf incited a riot against the Jem'Hadar, Toman'torax, in retaliation for threatening O'Brien. ()

The two did occasionally experience conflict. During the 2372 Guild of Restaurant and Casino Employees strike against Quark's Bar, Grill, Gaming House and Holosuite Arcade, Worf attempted to patronize the bar. A strong advocate for the interests of labor over capital, O'Brien intercepted Worf and attempted to persuade him not to cross the picket line. Their discussion became heated, escalating into a shouting match. When Dr. Julian Bashir attempted to intervene, a table was inadvertently shoved and Bashir ended up with a cut on his forehead. Worf, O'Brien, and Bashir were arrested by station security for brawling and spent the night in a holding cell. ()

In 2373, Worf and O'Brien participated in recovering a Jem'Hadar ship from Torga IV. Although Worf believed that Enrique Muniz would not survive from his wounds, O'Brien did not agree and clashed with Worf's pessimism. Worf was later proved right and Muniz did pass away. Once the mission was over, O'Brien and Worf performed the Klingon tradition of ak'voh in front of Muniz's casket. ()

O'Brien had to undergo a ritual fasting with Julian Bashir and Sisko as part of Worf's Kal'Hyah ceremony, which was different than what he thought it would be. He couldn't last the four days (even vowing to kill Worf at one point), and when he heard the wedding ceremony was called off, he and Bashir immediately ordered a large feast of Terran and Bajoran food. Sisko stopped them and helped put the wedding back on track. ()

At one point, Worf and O'Brien, while watching Jadzia and Quark playing a game of tongo against each other and a group of Ferengi waiters, Worf made a bet that Jadzia had the game in hand. He wagered to O'Brien that if she won, he would owe Worf a bottle of bloodwine. If Jadzia lost, Worf would then owe the chief a bottle of Scotch whiskey. In the end, Worf ended up saying that he would need time to come up with O'Brien's payment. ()

After Jadzia Dax died at the hands of Gul Dukat, O'Brien was one of the first people who attempted to cheer up Worf. While drinking bloodwine and reminiscing about old crewmates from the Enterprise (most notably, Reginald Barclay), O'Brien found out what was bothering Worf – the fact that his wife did not die an honorable death, and thus could not enter Sto-vo-kor. O'Brien then directed Martok to help Worf, who assigned him the mission to destroy the Monac IV fleet yards. ()

A short time later, O'Brien helped Worf ease his hostility to Ezri. Over a bottle of bloodwine, O'Brien asked how Jadzia would feel if she knew how poorly Worf treated Ezri. When Worf claimed that there was no way to know, O'Brien refuted the claim, suggesting he talk to the one person Worf had been avoiding. After keeping her in Starfleet, Worf and O'Brien attended Ezri's promotion party. ()

When O'Brien's authorization code was used to access sixteen cases of bloodwine sent to Martok by Sirella, Martok, and Worf had to quiz O'Brien on where the cases went. O'Brien had to explain to Worf and Martok that Nog must have taken the bloodwine to barter for a graviton stabilizer. Worf and Martok gave O'Brien one day to find the bloodwine. Fortunately, Nog had returned with sixteen cases of 2309 bloodwine bought from his cousin Gant, an even better vintage than the ones Nog took. Both Klingons gave O'Brien a bottle of the bloodwine as an "apology". ()

Benjamin Sisko 
O'Brien's relationship with Benjamin Sisko could be described as a classic example of a crewman's loyalty and devotion to a commander. And this relationship developed quickly. O'Brien respected Sisko from the first, and Sisko came to rely on Miles to keep Deep Space 9 running in the earliest days of his command.

Sisko was quick to reprimand O'Brien, after the Tosk incident, even though he approved of O'Brien's actions on a personal level. ()

Aside from this incident, Sisko seemed to have developed a very casual friendship with O'Brien, despite the difference in their ranks and the fact that Miles was an enlisted crewman and Sisko an officer. And O'Brien was unswervingly loyal to his commander. They both would talk about their respective roles as fathers. ()

Sisko verbally threatened the Cardassians should any harm come to O'Brien, who was held under false charges. Upon concluding the Cardassians' plot regarding the Maquis, he pulled a few strings and extended O'Brien's vacation time. ()

O'Brien volunteered to remain behind on Deep Space 9 to help Sisko, Li Nalas, and a handful of others retain control of the station after Starfleet was ordered off by the Provisional Government, under the influence of The Circle. He did this even though it could have meant the end of his Starfleet career and over the strenuous objections of his wife. ()

Sisko was sympathetic to O'Brien after his daughter Molly was thrown in a time portal. Once the incident ended, he volunteered to represent his engineer at a Starfleet hearing, and defended his actions at a hearing. ()

Odo 
Miles O'Brien and Odo had a good working relationship. Odo volunteered to represent O'Brien when he was tried in a Cardassian court, successfully proving O'Brien's innocence despite the Cardassian legal structure regarding the trial as a mere formality for a pre-determined sentence. This trial gave Odo the opportunity to get to know O'Brien better and develop an admiration for his strong sense of duty when he proclaimed that he had always tried to be somebody his children could be proud of. A couple of years later, he allowed the O'Briens to return the temporally-displaced Molly O'Brien to Golana, even though they broke her out of a holding cell. He joked that he was actually disappointed as he expected O'Brien to succeed in breaking someone out of the station without being discovered. ()

At one point, Garak makes mention that O'Brien shares "human crime novels" with Odo; he states that they may be influencing Odo's thinking. ()

O'Brien and Odo once went kayaking in a holosuite; an activity Odo found "quite enjoyable". ()

Kira Nerys 

O'Brien's relationship with the Bajoran first officer of Deep Space 9 started out rocky. Kira did not trust Starfleet, or the presence of the Federation on DS9. But, O'Brien earned her trust, and her friendship.

The turning point in O'Brien's relationship with Kira came when he helped her rescue Li Nalas from a Cardassian prison camp. From this point, Kira began to view O'Brien as someone she could trust, and someone she could rely on in a dangerous situation. ()

Kira carried Miles and Keiko O'Brien's baby to term following a runabout accident that threatened Keiko's pregnancy. The fetus was transferred to Kira's womb under the emergency circumstances so that both mother and child might live. During Kira's pregnancy, she and Miles formed a close, even intimate personal relationship. Kira was invited by Keiko to live in the O'Brien's' quarters, and Miles helped Kira with the pregnancy's physical discomfort with massages and other Bajoran treatments. The physical and emotional closeness of this time caused O'Brien and Kira to struggle against romantic feelings that developed between them, although in the end they were able to put those aside and remain friends, Kira retaining an aunt-like relationship with O'Brien's children. ()

Interests and hobbies
During his childhood, Miles developed keen construction skills. Despite doing poorly in mechanical aptitude tests, he spent many hours constructing model starship engines, models of subspace transceiver assemblies and ships in a bottle. He also did a great deal of hiking, climbing mountains in his native Ireland. (; ; )

O'Brien's one continuing passion was kayaking, and he frequently found himself visiting sickbay or the infirmary for shoulder injuries sustained during programs. (; ) This eventually resulted in humoral socket replacement surgery in 2371 (although the injury that necessitated the operation was not sustained through the sport). This did not end O'Brien's shoulder problems – he suffered a torn rotator cuff four years later, while practicing baseball with the Niners. ()  He enjoyed singing while kayaking, which he felt helped establish a good paddling rhythm. ()

Together with Julian Bashir, O'Brien pursued several other hobbies like racquetball, darts and historical reenactments in the holosuite of events such as the Battle of Britain, the Battle of Clontarf, or the defending of the Alamo, of which he even created a detailed model in his quarters. ( et. al)

He maintained his love of music, playing the cello in a string quartet aboard the Enterprise. () O'Brien was also a fan of detective fiction novels, particularly Mickey Spillane and his character Mike Hammer, a preference he passed on to Odo, to whom he frequently loaned books. ()

O'Brien was literate in the Trill language. ()

A favored drink of O'Brien's was coffee: Jamaican blend, double-strong, double-sweet, as well as just black and double-sweet. He was in the habit of drinking it throughout the day, although until 2370 Keiko was under the impression he didn't drink it in the afternoon.  ()

O'Brien was a fan of Starfleet combat rations, and that those rations were the only thing that he missed about the Cardassian front. (; )

According to Sarina Douglas, she thought O'Brien would be a fitting replacement for Greek god Atlas if he ever got tired, adding that "he would do it with a smile on his face." ()

Holograms 

Miles O'Brien has been holographically duplicated on a number of occasions.
A recreation was used by Romulans to see if a brainwashed Geordi La Forge would kill on command in 2367. ()
A recreation was created by the personnel of Deep Space 9 in order to lure Bajoran soldiers into a holosuite during the coup d'état attempt by The Circle. ()
A transporter accident in 2372 aboard Deep Space 9 resulted in transporter patterns that would normally be stored in the pattern buffer to overwrite some of the characters in the Julian Bashir, Secret Agent 1960s holoprogram. The character of Falcon was overwritten with the appearance of O'Brien. O'Brien later willingly played the character of Falcon with Bashir during their off hours. ()
Luther Sloan recreated the entire station, and staff, of Deep Space 9 in 2374 as part of his investigation into Julian Bashir. This program had a recreation of O'Brien. ()

Alternate realities and timelines 
In the anti-time past created by Q, O'Brien was puzzled by Captain Jean-Luc Picard's knowledge of his hobby building model ships in 2364. The time traveling Picard learned this information about O'Brien in a conversation two years later. ()
In an alternate timeline created when the  crashed on Gaia in the 22nd century, O'Brien married Rita Tannenbaum and they had many descendants, including Miranda O'Brien and their great-great-great-great-great-granddaughter . The name "Molly" was passed down through the O'Brien family over the course of approximately two hundred years. ()
In 2371, O'Brien experienced a series of alternate timelines after becoming infected with delta-series radioisotopes following an accident aboard the station. This, coupled with the presence of a cloaked Romulan warbird nearby, had the effect of shifting him forward in time by several hours. O'Brien's return to the present altered the course of the future events that he witnessed. ()
In the first timeline, O'Brien was killed by a high-energy laser. After witnessing the event, O'Brien and Odo checked out the location, but found no sign of the device having been planted yet. A surveillance device was eventually discovered implanted in the bulkhead by a Klingon covert strike force. Aware of his fate in this timeline, O'Brien made sure to avoid this location at the time that he would die. ()
In the second timeline, O'Brien died due to the damage that the radioisotopes did to the basilar arteries in his brain stem which was not discovered until Dr. Julian Bashir performed an autopsy on him. Bashir warned the time-displaced O'Brien who had the past Bashir perform a basilar arterial scan, allowing him to fix the damage in time. ()
In the third timeline, O'Brien witnessed the destruction of DS9 and his future self leading survivors to safety in the station's runabouts. ()
In the fourth timeline, O'Brien deliberately contaminated himself further in order to determine the exact cause of events he had witnessed, traveling into the future by 3.5 hours and witnessing the warbird destroying the station. However, the original O'Brien succumbed to the radiation poisoning and he was replaced by his counterpart from the timeline that he had visited. Thus, events that occurred to O'Brien from this point on involved the future version, rather than the O'Brien from the original timeline. By warning the crew about the warbird attack, O'Brien was able to avert this timeline. ()
 In an alternate timeline created by Q where Earth had become the Confederation of Earth, Miles O'Brien was a general in the Confederation Corps and by 2401, was the field officer fighting the Dominion Alliance War. ()

Appendices

Appearances 
 
  (Season 1)
 
  (Season 2)
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  (Season 3)
 
 
 
  (voice only)
 
 
 
 
 
 
 
 
  (Season 4)
 
 
 
 
 
 
 
 
 
 
 
  (Season 5)
 
 
 
 
  (Season 6)
 
  (Season 7; anti-time version)
 
 Miles O'Brien appeared in all episodes of DS9 except:
 
 
 
 
 
  (mirror counterpart appeared)
 
 
  (Colm Meaney portrayed Albert Macklin)
 
 
 
  (mirror counterpart appeared)
 (Hologram)

Background information 
Miles O'Brien was played by Colm Meaney in all appearances. When asked what he thought O'Brien brought to the show, during an interview in November 2009, Meaney replied, "I don't know. I think… you know, because of that world that we inhabited, with all of these extraordinary characters who could do extraordinary things, there was a terrific kind of humanity in O'Brien… and that's due to the writing, of course, but it's also in every sense, in that he was humanoid! But I think he brought that kind of contemporary sensibility to an extraordinary world, and it's nice to be able to say that. And, of course, we had the storylines with Rosalind Chao, who played my wife, Keiko, which were great, just to be able to play those storylines of domestic tension or the problems facing a kid in that environment." 

Prior to revealing his first name "Miles" in the TNG fourth season episode , Ronald D. Moore and the other writers considered "Aloysius" as a first name for O'Brien. ("Namely O'Brien", ) Commented Rick Berman, "I named him after my nephew, whose name is Miles O'Brien." (The Fifty-Year Mission: The Next 25 Years, p. 442)

On bringing Meaney and thus O'Brien to DS9, Michael Piller stated, "We've always thought he was a terrific performer and now we're giving him something much more interesting to do as a leading character on the new show. He is pulling hair out from one minute to the next because everything is breaking down. He can't get the replicators to make a good cup of coffee; his wife Keiko is terribly unhappy about having been taken off the Enterprise and over to this dreadful station. So he finds himself in an uncomfortable position." (Trek: Deep Space Nine: The Unauthorized Story, p. 11) Contrasting the portrayal of O'Brien in TNG with how the character is depicted in DS9, Meaney himself commented, "He's essentially the same character [….] I haven't really changed my approach to playing the character. He's just the same guy trying to deal with many more problems." (The Official Star Trek: Deep Space Nine Magazine issue 1, pp. 22 & 23)

According to DS9 executive producer/writer Ira Steven Behr, "O'Brien is every man. In a show about humans and aliens, he's as Human as you get." Similarly, Behr's writing partner for the first four seasons of the show, Robert Hewitt Wolfe, says, "He's just a regular guy, a guy doing his job. He's just the most unlikely of all heroes because he's a family man with a daughter and eventually a son and a wife and they have arguments and a real relationship, and he's just a working class schmo, I mean obviously he's a really bright guy and very good at what he did, but basically, a working class schmo just trying to get through his day." (Crew Dossier: Miles O'Brien, DS9 Season 5 DVD, Special Features)

The DS9 writing staff had a running joke where the character would suffer significant trauma in at least one episode per season. Among these were , , ,  and . () According to Ira Behr, "Every year in one or two shows we try to make his life miserable, because you empathize with him." Robert Hewitt Wolfe further explains, "If O'Brien went through something torturous and horrible, the audience was going to feel that, in a way they wouldn't feel it with any of the other characters. Because all the other characters were sort of, I wouldn't say larger than life, but nobler than life, but O'Brien was just a guy, trying to live his life and so if you tortured him that was a story." (Crew Dossier: Miles O'Brien, DS9 Season 5 DVD, Special Features)

The relationship built up on DS9 between O'Brien and Bashir was very important to all of the writers, as well as both actors. According to Ronald D. Moore, after the scene where they sing the British patriotic hymn "" together in , all of the staff writers wanted to write scenes involving their friendship. Alexander Siddig says, "it's been said, by even the producers, that O'Brien and Bashir are the only real friendship that's ever happened on Star Trek. These two really are friends. It's not like some kind of odd couple scenario, like Spock and Kirk. It's a real friendship. These people talk about inane things, and I think that's been really refreshing." Robert Hewitt Wolfe elaborates, "It was just great. There was just great chemistry between the two actors, great chemistry between the two characters. It was brilliant of Michael and Rick to create these two characters as foils for each other. And to then see this relationship develop over the years till they're best friends, till Miles actually likes Bashir kind of almost better than his wife some days, which is very real, I mean there's days that everybody, you know, it's easier to be friends with a friend than with your wife some days." (Crew Dossier: Miles O'Brien, DS9 Season 5 DVD, Special Features) Ira Behr goes even further, and cites it as his favorite relationship in all of Star Trek; "The relationship between Bashir and O'Brien is the best relationship, the best friendship, in the history of the franchise. Spock and Kirk were still about the captain and his number one. This is a friendship with two equals, two guys. It's a wonderful thing to watch how this relationship has grown." (Crew Dossier: Julian Bashir, DS9 Season 6 DVD, Special Features)

Trivia 
O'Brien is one of two enlisted characters in Star Trek to have received any significant character development, the other being Yeoman Janice Rand.

O'Brien is one of five characters to appear in two series premieres ( and ), the others being Jean-Luc Picard (same episodes as O'Brien), Quark, Morn, and Broik (in both  and ).

O'Brien is one of four characters to appear in two series finales ( and ), the others being Worf (same episodes as O'Brien), William T. Riker and Deanna Troi (both in  and ).

O'Brien is the only character to appear in two series premieres and two series finales, ( and ), and ( and ).

Problematic rank history 
The character of Miles O'Brien, and the exact rank he held in Star Trek, has a history of its own spanning the length of the character's existence. 

In thirteen years of the character's appearances, only in the last four was his rank established to be presumably senior chief petty officer (although this term was never directly used on screen). Through various other stages of the character's development, O'Brien was referred to as a crewman, a lieutenant, and various script notes indicated he was a "warrant officer."  The ization of  indicated O'Brien held a rank known as "ensign junior grade". 

The exact history of O'Brien's ranks are as follows:

1987: Appears in  and is referred to as "Conn" (not as a name, but showing he was conducting the movements of the ship). In this episode, O'Brien wears the single pip of a Starfleet ensign (1) and a red command division uniform. In  he appears again, with no apparent insignia, credited as First Security Guard and in the corresponding yellow operations division uniform.

1988: Appears in , credited as Transporter Chief. He wears the two pips of a Starfleet lieutenant (2). In  he appears wearing the same uniform and insignia as "The Child" and is directly addressed by Commander Riker as "lieutenant", seemingly indicating that O'Brien is an officer.

1989: O'Brien's surname is mentioned for the first time in . He is wearing the two pips of a Starfleet lieutenant again and is addressed as chief.

1989: Appears in , again wearing two pips. Toward the end of the episode, then Lieutenant junior grade Worf gives him transporter coordinates. After entering them, Worf says "I relieve you", to which O'Brien replies, "Well I… yes, lieutenant", which is the correct way to formally address someone of inferior rank (if Worf had been his superior, it would likely have been "sir"). There have been multiple examples in Starfleet of position trumping rank, such as a bridge officer being left in command of a ship, even when a superior officer is on duty in engineering.

1990: Appears in  and is addressed as "another chief petty officer" by Sergey Rozhenko, even though he is shown wearing lieutenant's pips, and is given a first (and middle) name, three years after his first appearance. From this point on, O'Brien's character is developed as a senior enlisted member of the Enterprise crew, although he continued to wear the lieutenant's insignia.
 Ronald D. Moore commented, "O'Brien was originally just a day player on TNG and very little, if any, thought went into his rank or background for quite a while. He officially became a Chief Petty Officer in "Family" when I wanted he and Worf's adoptive father to both be non-coms in contrast to Worf. Making him an enlisted man seemed to give us another color in the show and to open up another window into Starfleet that we hadn't explored before."  

1991: Appears in  wearing his usual uniform and insignia. At the end of the episode, O'Brien wears a dress uniform also with the two pip insignia of a lieutenant. Later in , he mentions Ensign Locklin to be "one of his technicians", once more suggesting a higher rank in line with his two rank pips. 

1992: Appears in  where O'Brien is given direct orders by Reginald Barclay (who is a lieutenant junior grade) thus firming up the idea that O'Brien is a noncom as opposed to an commissioned officer. This episode marks the first time that O'Brien wears the single hollow pip with his regular uniform (3). (The  defines this as the insignia of a "chief warrant officer", although the term is never used on-screen.)

1993: Appears in , where he transfers to Deep Space 9 to take a new position as its "chief of operations". In , this transfer is described as a "promotion". For the next three years, O'Brien wears a single hollow pip insignia with his rank again very much in question. Script notes from several Deep Space Nine episodes indicate he is a "warrant officer", while the pilot's novelization states O'Brien is an "ensign junior grade" (3).

1994: Appears in  where he briefly describes the history of how he became tactical officer and "got [his] gold suit" on the . In the next episode, , his title is stated to be senior chief specialist. He appears also in the past segment of  wearing the single pip of a Starfleet ensign, which is consistent with what was worn during "Encounter at Farpoint" (1). The  incorrectly reports that O'Brien wears a single hollow pip during the episode.
 In , O'Brien told  he was Chief Engineer of Deep Space 9, rather than Chief of Operations.
 In , after Nog passes the entry exam for Starfleet Academy, O'Brien mentions to Bashir that if Nog graduates from the Academy, he [O'Brien] will have to address Nog as "sir." Despite this, Nog (upon becoming an ensign) still referred to the chief as "sir."

1995: In , when the other officers are lamenting having to attend a formal Starfleet function, O'Brien is asked if he would like to attend. He half-jokes, "Full dress uniform, fine table linens, a different fork for every course? No thanks, that's why I stayed an enlisted man. They don't expect me to show up for these formal dinners."

1995: By the time of , O'Brien has begun to wear a new insignia reminiscent of the chevron rank used by modern-day master chief petty officers in the US Navy (4). In this episode, a Jem'Hadar familiar with Starfleet insignia identifies it as a chief petty officer insignia. Presumably it was actually senior chief petty officer, as the word senior was used in "Shadowplay", so the Jem'Hadar presumably simply left out the distinction. His dress uniform in  displays no rank insignia, but in  it has the single hollow pip.

Possible explanations for O'Brien's various titles and insignia include:

During some points of The Next Generation, O'Brien may have held a field commission as an officer, which would explain why Riker once called him a lieutenant. His continuous wearing of two pips (which is the standard insignia of a lieutenant) might be a type of "honorary insignia" even though he was later clearly referred to as a chief petty officer.
Starfleet non-commissioned officer insignia might be identical to officer insignia, with the number of pips worn by an noncom indicating level of seniority as a chief petty officer. Under this system, one pip would equal a chief petty officer, two a senior chief, and three a master chief. With O'Brien wearing two pips throughout The Next Generation, this would equate with his final rank of senior chief petty officer in Deep Space Nine.
Ranks for starbase personnel may simply differ in name from personnel serving on starships.
The original intention for warrant officers (senior enlisted personnel) in the old British system most Western militaries take their traditions from, was that they held a "warrant" entitling them to the same authority of a commissioned officer but within the narrow field in which they are an expert. Thus, a transporter "chief" may, with respect to the operation and maintenance of transporters, hold a warrant granting the same authority as a lieutenant and therefore he may wear the rank insignia designating him as such.  This could explain the slight hesitation he displayed in the 1989 episode "The Emmisary" where Worf, a Lieutenant JG, relieves him.  Normally in the operation of a transporter, his authority may supersede Worf's , but as a commissioned officer, Worf may have held a more general authority and was exercising that.  His response to Worf is the correct formal response of a superior rank to a junior who, is by nature of position or authority, relieving him.
In Kayshon, His Eyes Open, it is suggested that oftentimes when a character appears with the incorrect number of pips, the additional pip is a kernel of corn. Although O'Brien's rank pips are clearly actual pips and not kernels of corn, this line may have been a tongue-in-cheek attempt to explain away such inconsistencies as O'Brien's. However, this would only potentially reduce his rank insignia to that of an Ensign and does not resolve the inconsistency of either him being explicitly called Lieutenant or his later-stated status as a non-commissioned offer.

Some problems with assuming that O'Brien is a Starfleet chief petty officer include:

The entire backstory seen in  reveals that O'Brien was once a senior department head officer under the command of Captain Benjamin Maxwell. With O'Brien being a chief petty officer on board the Enterprise, it stands to reason that he was either a very junior CPO or perhaps even an ordinary petty officer under Maxwell. With the duties O'Brien was stated to have held (tactical officer), this creates a problem since nowhere else in Star Trek has an enlisted person been seen holding such a high-level position. It is important to note that O'Brien's service under Maxwell occurred during the Federation-Cardassian Border War. Under wartime conditions, lower ranked officers and perhaps even non-commissioned crew members may have been pressed into service in places where they would not otherwise have the opportunity to serve during peacetime.
At one point, O'Brien appears to have had officers working for him. Such was the case in , in which O'Brien states that an ensign was "one of his technicians". This may be explained by O'Brien holding a type of "positional authority" which would grant him authority to officers due to his position as transporter chief, even though he was militarily junior. This continued well into his tenure on Deep Space 9, with an ensign in  addressing him as "sir", several members of his staff appearing to be ensigns or lieutenants and Nog clearly being subordinate to O'Brien despite holding the rank of ensign. However, in the whole DS9 series, it is continuously stated that O'Brien is chief engineer of the station and as mentioned above this position often trumps the rank someone holds. However, as also noted above, nowhere else in Star Trek has such a position been held by an enlisted person, and unlike his position on the Rutledge, most of his service on DS9 (including his initial assignment) occurred during peacetime.
Julian Bashir once remarked in  that O'Brien had attended Starfleet Academy, which is a training school for commissioned officers and not noncoms. Ronald D. Moore remarked, "This is a mistake, plain and simple. If you want to rationalize it, I suppose we could say that the enlisted training program also takes place at the Academy."  The idea of Starfleet Academy training enlisted personnel was also backed up by statements of Simon Tarses in .

Apocrypha
In post-finale   and novella The Lotus Flower, O'Brien relocates from Earth to Cardassia in the year after DS9 ended.

In the Star Trek: Typhon Pact novel Raise the Dawn, O'Brien is reassigned as chief engineer following the destruction of Deep Space 9 in 2383 of both the ground-based facility that substituted for it and supervising the Starfleet Corps of Engineers in the construction of the new, replacement station.

In the Star Trek: The Fall novel Revelation and Dust, O'Brien takes over as chief engineer of the new Deep Space 9 after its construction was completed.

The alternate reality version of Miles O'Brien appears in the Star Trek: Ongoing story arc The Q Gambit in which he is a member of the Free Federation Resistance with the rank of lieutenant and is first officer of the , with his wife Keiko as captain of the Defiant. He rescues Sisko, Odo, , , and  from Changelings after they had murdered Chancellor Worf using a shuttle and when they get back to the Defiant, O'Brien is assisted by Scott in fixing the ship's warp drive during which the two of them discuss and bond over their mutual love of engineering.

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