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Catherine Elizabeth Halsey
Biographical information
Date of birth

March 19, 2492[1]

Physical description





Approximately 1.7m[3]


M6 Pistol, unknown model


A.I. Jerrod.

Hair color


  • Blond (As depicted in Halo Legends)
Eye color


Chronological and political information

Human-Covenant War

Notable Facts
  • Is one of the smartest women of the 26th century[4]
  • Types at a rate of 140 words per minute.[5]

UNSC Naval Intelligence

Spartans never die? If only that were true.[6]

Catherine Elizabeth Halsey, M.D., Ph.D., (Civilian Consultant 409871) is a praised scientist and employee of ONI, best known for her work with the SPARTAN-II super soldier and MJOLNIR armor programs. Despite being a civilian, she held considerable authority within ONI and commanded considerable respect from many military figures.[7] Publicly, she was well regarded, in particular due to the high esteem she felt for her Spartans and guilt she endured from condemning them to the life of a super soldier.




Early Life

Not much is known about Dr. Halsey's early life, but what little is known gives a glimpse of what would be a promising career. In her own words, she was "...smarter than her parents, always reading, talking, learning, and eager to share her knowledge with anyone who would listen."[8] By the age of 15, Dr. Halsey was already writing her second Doctoral Thesis paper, in which she discussed archaic line commands.[9] It is also known that at some time in her early life, she supervised the creation of the template for third-generation Smart AIs.[9] She was also Vice Admiral Ysionris Jeromi's star pupil.[10] It should also be noted that her personality and appearance are very similar to Cortana's, since Cortana was created from Halsey's mind.

ONI Projects

Main article: SPARTAN-II Project

Dr. Halsey served as scientific advisor for to the Office of Naval Intelligence from 2515 to 2522 when she was made Chief scientist.[1] She made huge contributions to many ONI Section III projects, including the creation and deployment of AI constructs. She also created and initiated the SPARTAN-II project as well as the development of the MJOLNIR Armor Systems. These all proved to be important developments for the UNSC, and to the continued survival of mankind.

"This boy could be more useful to the UNSC than a fleet of Destroyers, a thousand Junior Grade Lieutenants -- or even me. In the end, the child may be the only thing that makes any difference."
—Catherine Halsey speaking to Lt. Jr. Grade Keyes, referring to John-117, in Elysium City.

Dr. Halsey was the creator of the SPARTAN-II project, and she built a set of rigorous genetic requirements that any potential candidate of the program was required to meet. From these requirements, she identified 150 candidates, but ONI would only give her funding to train 75 of them. She met each of the candidates and determined who the 75 would be. She had Junior Lieutenant Jacob Keyes accompany her in the interview of John-117. She then had the children secretly brought to the planet Reach for training. The 'recruited' children were replaced with flash clones, who died soon after.

Halsey overlooking Daisy-023's Spartan augmentations.

With the assistance of Chief Petty Officer Franklin Mendez and the AI Déjà, she proceeded to train the Spartans. She supervised their augmentation procedures, combat training, and education, and studied the effects of the Spartan lifestyle on the children. She kept in close contact with them all throughout their lifetimes, from her base under Reach. Annoyingly, she was always able to tell them apart from each other, even under half a ton of MJOLNIR battle armor. Dr. Halsey always used their first names, never their ranks or Spartan tags. This showed she had a huge amount of respect for, and from, the Spartans; she was also able to order them around and the Spartans referred to her as "Ma'am", which is another example of how they respect her, not to mention that they also regard her as a sort of a mother figure. She also knew many of the Spartans' closely held secrets, having taught many to them as children, such as the Oly Oly Oxen Free security tune.[2]

Involvement during Human-Covenant War

Battle of Harvest

After first contact with the Covenant, Dr. Halsey accessed LCDR al-Cygni's ONI Sloop Walk of Shames data archive. During Dr. Halsey's investigation, she began researching the last conversations of the A.I. Mack, and his choice of misspelled Shakespeare during his last days of rampancy. Dr. Halsey was conducting her research under the name Charlie Hotel.

The Package

Halsey and John face a Major Elite on a Covenant Assault Carrier.

At some point between the battles of Chi Ceti and Reach, Halsey was captured by a Covenant Fleet, while cryogenically frozen. A team of Spartan-IIs consisting of John-117, Kelly-087, Frederic-104, Solomon-069, and Arthur-079 were sent to rescue her with Open Frame 92/Extra-Vehicular Activity vehicles. Knowing Halsey's value to both the UNSC and the Covenant, the Covenant Fleet Master planted decoys in several CCS-class Battlecruisers.

Solomon was killed by one of these decoys, which turned out to be an Antimatter Charge. Arthur was also killed, crushed between two cruisers while covering Kelly-087 from Seraph fire. After finding the ship Halsey was on, John, Kelly and Fred fought through large numbers of Covenant forces, though Fred and Kelly were separated during the fight, leaving John to think them dead. John finally reached Halsey and rescued her, but they were stopped by an Elite Major. Halsey then watched as John engaged the Elite in an Energy Sword duel. However, the Fleet Master in command of the Covenant Fleet detached the section of the ship they were in, returning the Major mid-fight via Gravity Lift and jumped to Slipspace.

Halsey and John soon made it to a Covenant Escape Pod, but were engaged by Seraph-class Starfighters. She was visibly frustrated at the slow speed of the pod, going so far as asking John to take out the Seraphs with just his Assault Rifle. They were soon rescued by Fred and Kelly, who had captured a Seraph, and later by the stealth ship that had deployed the Spartans. Later on the stealth ship, Halsey comforted John as he swore not to lose another Spartan.

Battle of Reach

Dr. Halsey's ONI memorial plaque.

In 2552, when the Covenant attacked the Reach Military Installation, Dr. Halsey was working in ONI's CASTLE Base. She volunteered to remain behind to ensure that all UNSC technology was secured from possible capture.[11] She initiated Operation: WHITE GLOVE, destroying several AIs (including Cortana's "older sister" Kalmiya) to keep the Covenant from accessing UNSC databases. With expectations that the Covenant would glass the planet and knowledge that even if they didn't, she would be facing an entire army of Covenant ground forces, it was clearly an offer of sacrifice.

However, this changed when Spartans Fred-104, Kelly-087, Vinh-030, Isaac-039, and Will-043 appeared at the entrance to CASTLE Base. With the firepower to potentially fight their way out, the possibility of surviving CASTLE Base's destruction became available. She gave emergency aid to the Spartans for their injuries, but a data anomaly detected by her accompanying AI, Kalmiya, attracted Dr. Halsey's attention.

The data had been accessed by Araqiel, an AI that worked for Colonel Ackerson, one of Dr. Halsey's main competitors within ONI. After tracing the data access, Dr. Halsey stumbled across the AI, left behind by its master. Araqiel then proceeded to threaten her (he went as far as telling her he would fill the room with poison, and that she would be reported). She started typing in "archaic line commands" to access his code directory and personal fail-safe. She then shut him down.[12] After shutting it down, she proceeded to read through Ackerson's files and discovered a number of things including the location of Onyx, evidence of the SPARTAN-III program and a map of the mining tunnels CASTLE base had been built upon. The latter particularly interested the Doctor as the file had been classified at X-Ray level, making the file abnormally important for ancient maps. From this, she deduced that there was something of importance under the mountain.

Assuming that at the very least these maps provided a back door, she chose to move the Spartans out of the base and into the mine shafts. She then triggered CASTLE Base's self-destruct mechanism and activated the fail safe on Kalmiya. With the Spartans in tow, they moved into the mine shafts.

Over the course of the next five days, the Spartans and Dr Halsey searched the mines, looking for either an exit or what Dr. Halsey would dub "the most important discovery of the millennium". On the fifth day, Fred discovered an entrance into a large Forerunner structure, and within, the Forerunner Crystal. However, the acquiring of the crystal sent a spike of neutrino radiation, attracting the attention of the Covenant. Their location was now threatened by Covenant forces.

Following a Covenant attack, Halsey and her team retreated into a hallway and sealed off the entrance, losing contact with Isaac and Vinh in the process. However, they quickly discovered that the hallway was a dead end. It is presumed that Halsey and the surviving Spartans remained stranded at this location for some time.

Days later, a group of Spartans, including John-117, rescued Dr. Halsey and the remaining Spartans and evacuated them from Reach to the captured Ascendant Justice.

Dr. Halsey later saw the importance of destroying this artifact after it caused a Slipspace anomaly that nearly resulted in the destruction of the Ascendant Justice. After escaping Reach, the group fled to the asteroid belt that the Spartan's first mission had been in. While there, she stole the rebel governor's spacecraft and, along with Kelly-087, whom she had sedated, escaped into Slipspace. When asked by Admiral Whitcomb as to the reasons for her actions, she gave a simple UNSC code Three-Nine-Two, which meant that she was on a high priority mission. She entrusted the Forerunner Crystal to Corporal Locklear, telling him to keep it safe, hidden, and to do whatever it took to keep it from falling into enemy hands, otherwise the Covenant would be able to go a hundred times faster in Slipspace. The Corporal destroyed the crystal, which is not totally against her orders, and died as a result of the explosion created by the destruction of the Forerunner Crystal. The Covenant later recovered a few fragments.

In the aftermath of the battle, she was presumed dead by the Office of Naval Intelligence and honored, with other personnel, on a plaque at ONI Alpha Site. It can be assumed the SPARTANS and Johnson neglected to report her retrieval from CASTLE Base then her following kidnap of Kelly and apparent desertion from the UNSC. Another possibility is that her name was added to the wall after the Battle of Reach but before the Spartans returned to Earth.

Battle of Onyx

As revealed in Halo: Ghost of Onyx, Dr. Halsey and Kelly eventually arrive at Onyx, while reuniting with SCPO Mendez and eventually her remaining SPARTAN-II's and the SPARTAN-III's. She helps decipher the mystery of the planet. At first, she tried to maintain secrecy about her intentions out of habit, until Kurt-051 confronted her about it. She admitted that she was not actually looking for weapons, but rather the secret Forerunner Shield World which she believed to be equivalent to a bomb shelter and would be capable of keeping the remaining Spartans safe to evade all current war and let them live to fight another day. Her relative expertise with Forerunner technology was vital to the survival of the UNSC forces on Onyx. At the end of the Battle of Onyx, she, along with Mendez, Blue Team, and the Spartan-III survivors, found herself inside the Shield World, which she believed was actually a Micro Dyson Sphere. Her fate is not yet known at this present time, though she is believed to still be trapped within the Shield World, along with the remaining Spartan-II's, Spartan-III's, and SCPO Mendez.


Little is given in the terms of social activities or even a list of friends. Her intelligence is unquestionable as well as the loyalty and respect she receives from the majority of her comrades and her Spartans. However, as seen in Halo: First Strike her judgment is not always correct, although bearing the guilt of the Spartan program, her sense of right and wrong has differed greatly. It is obvious that she truly cares about her Spartans.  She has a notable fondness for classical music, especially Debussy, and often asks nearby AI's to play select pieces as she works.[13]

What can be gleaned is that she preferred the company of AI's, and although she may be angered easily at being mentally defeated, always appreciates the simplicity of them. None more than Cortana, who was actually created from a flash clone of her own brain. She is an atheist, lacking belief in any god.[14]

Halsey's Guilt

Dr. Halsey carried extraordinary guilt because of the SPARTAN-II project, and she felt that she had exploited the children and destroyed their lives. Though she continued to support them and gain monumental prestige for her efforts, she also felt responsible for each one who died. She never could quite justify their exploitation as a "necessary sacrifice." She also had considerable respect for the Spartans, and addressed them by their first names (even with their armor on), which seemed to greatly annoy them.

Her feelings of guilt were made evident by the fact that she often referred mentally to "sacrificing the few to save the many," though this rarely worked to soothe her conscience. By the time she was rescued from Reach by the Ascendant Justice, she simply wanted to save as many lives as she could, believing that the war was not one that the UNSC can possibly win.

While she knew that her own Spartans, the SPARTAN-IIs, couldn't be persuaded to turn from the war, she believed the SPARTAN-IIIs may not yet have been fully determined to win the war, and set out to try and weaken their resolve to fight. In addition, she decided to hand over data concerning Avery Johnson and how his Boren's Syndrome made him immune to the Flood to Master Chief since if she handed the data over to ONI, Johnson would likely be dissected in order to find a cure to the Flood infection.

She estimated that there is a billion to one shot that they can replicate Johnson's condition but ONI would do it to save Humanity from a greater foe. At first, Chief chose to sacrifice Johnson to save millions of people out of his duty to protect all of Humanity. At the end of Halo: First Strike, however, Master Chief reconsidered and eventually destroyed the data due to the sacrifice of Vice Admiral Danforth Whitcomb and Lieutenant Elias Haverson.


  • Catherine is around 60 at the time of the main Trilogy, though she would appear somewhat younger due to time spent in cryo-sleep.
  • Her pseudonym, "Charlie Hotel", is from the NATO phonetic alphabet, and refers to her first and last initials, which are C.H.
  • In Halo: First Strike, it is stated that Dr. Halsey was not keen on losing, as seen when she kept losing at a game of Twenty Questions with her training Spartans and soon quit playing.
  • She had a knack for embarrassing the Spartans with the way she was able to tell them apart through subtle habits in their postures, despite their identical MJOLNIR armor, something no other non-Spartan was able to do. Another interesting fact of her relationship with the Spartans is that she never referred to them by their numerical designations, always their names.
  • She had a bad habit of keeping a messy office and drinking cold coffee, tending to prepare the drink and then become distracted by work, only remembering it hours later.[15]
  • She served as a mentor to Professor Ellen Anders at some point prior to the events of Halo Wars, though they apparently had a major falling out, as noted by Anders in the manual, saying "Why mention Halsey here? She hated me and I hated her."[16]
  • After the Battle of Reach, she was presumed dead by the Office of Naval Intelligence, although no body was obviously found. She was mentioned in a memorial plaque inside the ONI Alpha Base on Earth.[1] This is odd, considering that John-177, Will-043, Fred-104, Cortana and Avery Johnson knew she had fled with Kelly-087. However, it is possible that the memorial plaque in question was erected before this news reached Earth.
  • She can type at an astonishing rate of 140 words per minute.[17]
  • She was possibly named after a side character, Catherine Halsey who appeared in the 1943 novel The Fountainhead, by Ayn Rand. However, this may be a coincidence.
  • She makes her first visual appearance in Halo Legends episode The Package, in which she appears to be contradictorily younger than she is in the books. Instead of black, graying hair, she is also depicted as having blond hair. However, the younger appearance could be due to time spent in cryo sleep which stops metabolism, effectively stops aging.
  • Two of Dr. Halsey's statements in The Package are references to similar statements made in the first two Halo games. She tells John-117 that she slept well "No thanks to their driving," which is echoed in Halo: Combat Evolved when he tells Cortana he slept well no thanks to her driving. She also tells John, "Don't make a girl a promise, if you know you can't keep it," which Cortana would tell him in Halo 2.
  • Halsey's appearance changes drastically from The Package to Homecoming. In The Package she is depicted as a fairly young woman with short hair and no glasses. Her appearance in Homecoming though is more based off her description from the books. It should be noted that various concepts in The Package, and Halo Legends in general, are considered an artistic license.



  1. 1.0 1.1 1.2 Halo 3: ODST map Alpha Site: memorial plaque
  2. 2.0 2.1 2.2 2.3 Halo: First Strike, page 119: As Fred's display compensated and enhanced the image, he saw it was human, slight of figure, female. She wore a gray pleated skirt and a white lab coat with a data pad stuffed into the breast pocket. He caught the glimmer of her eyeglasses, black-rimmed with faint bifocal lines. Her gray hair was coiled into a tight bun. But it was her face that caught and held his focus—he recognized the tight smooth skin that wrinkled only in the corners of her mouth and her gray-blue eyes. She was the intellect behind the SPARTAN-II program, and the one who'd invented their MJOLNIR armor. She was Dr. Catherine Halsey.
  3. Princess Monologue
  4. Halopedia letter to Eric Nylund
  5. Halo: Ghosts of Onyx, page 177
  6. Halo: First Strike, page 249
  7. Halo: First Strike, page 123: Dr. Halsey was only a civilian, but the Spartans had always accepted her authority. Perhaps because she had acted as an equal among the Fleet Admirals and Generals who were constantly trying to co-opt her work.
  8. Halo: The Fall of Reach pg. 235
  9. 9.0 9.1 Halo: First Strike, pg. 128: "These commands were invented, refined, and then discarded and forgotten long before even the first functional dumb AI went online," Dr. Halsey told him. "I learned them when I was fifteen, working on my second doctoral thesis." She smiled and said, "I supervised the creation for every third-generation smart AI on this planet. I know everything there is to know about you, including your borderline disregard for human life."
  10. Halo: The Fall of Reach pg. 57
  11. Halo: First Strike pg 125: "I volunteered to be the fail-safe option, she told Kelly. "In the lower levels of these caverns are enough high explosives to level the facility--in case we were ever overrun by the enemy. I'm here to make sure no one gets access to our technology."
  12. Halo: First Strike pg.127/128
  13. Ghosts of Onyx page 148
  14. Ghosts of Onyx, page 157
  15. Halo: The Fall of Reach and Halo: First Strike
  16. Halo Wars manual, character profiles.
  17. Halo: Ghosts of Onyx, page 177

This article uses material from the "Catherine Elizabeth Halsey" article on the Halo wiki at Wikia and is licensed under the Creative Commons Attribution-Share Alike License.


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