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Biographical information
Began service


Physical description

Female AI programming


Tall and slender with short-cut hair in Halo: Combat Evolved, then long hair in Halo 2 and Halo 3.

Normal color
  • Normal: Blue/Purple, Green while inside Alpha Halo's central computer.
  • Angry: Pink/Green[2]
  • Flattered: Pink
Political information and functions

United Nations Space Command

Primary function

Software Infiltration, Capture of a Covenant Prophet, Assisting the Spartans

Notable battles
Keep your head down, there's two of us in here now.

Cortana, UNSC Artificial Intelligence serial number CTN 0452-9, is a "smart" A.I. construct, or "Intelligent Agent". She was one of the most important figures in the Human-Covenant War, and served as John-117's partner in various combat missions, as well as serving as the A.I. for the United Nations Space Command Halcyon-class Cruiser Pillar of Autumn and the Orbital Defense Platform Cairo Station. In addition, she held vital data pertaining to the Halos, including the Activation Index from Alpha Halo.




Cortana was created using a flash cloned copy of the famous Dr. Catherine Elizabeth Halsey's brain. Twenty flash cloned brains were created, but only one survived;the survivor was used to create Cortana. The neural pathways of the cloned brain were scanned and copied through a process called Cognitive Impression Modeling.[3] She is one of at least two A.I.s that were created from Dr. Halsey's brain, the other being her predecessor, Kalmiya, another "smart" A.I.

Cortana seems to share her creator's memories, thoughts, opinions, and even values. When she was asked by Dr. Halsey to pick a "carrier", Cortana chose John-117 for their neural compatibility. She is not only a facsimile of Dr. Halsey's mind, but also a replica of her physical form, albeit at a younger age.

Fateful Meeting

Cortana first met the Master Chief prior to the Battle of Reach, when she was integrated into his new MJOLNIR Mark V armor. Together, Cortana and the Chief passed a test that was devised by Colonel James Ackerson. The test included armed ODSTs, anti-tank mines, automatic turrets in the razor field, and even a SkyHawk for an air strike. After the test, Cortana was installed into the Pillar of Autumn for the mission she was created for. While aboard, she took her revenge on Colonel Ackerson by hacking into his system and blackmailing him, hoping that this would send him back to the front lines.

Cortana's primary mission was to aid the SPARTANs in the infiltration of a Covenant vessel and the capturing of a Covenant Prophet. The UNSC would then try to bargain with the Covenant for a peace treaty.

The Battle of Installation 04

Main article: Battle of Installation 04

When the operation was canceled due to the Covenant's surprise assault on Reach, both Cortana and the Master Chief were able to fend off Covenant forces at Reach. They were eventually forced to flee the burning planet, heading to a random location as per the Cole Protocol. However, Cortana secretly inserted coordinates translated from symbols on a rock that Master Chief discovered on Sigma Octanus IV, thinking that they were of some significance to the Covenant.

After emerging out of Slipspace, the two discovered a ring shaped world called "Halo". Unfortunately, Covenant ships had followed them, and the fighting continued. Controlling the Pillar of Autumn's defenses, Cortana managed to destroy four Covenant targets over Installation 04 before the ship's weapons were disabled by Covenant boarders. Following the Cole Protocol, Captain Jacob Keyes, the ship's commanding officer, prepared to abandon ship. Because the Cole Protocol forbade the capture or destruction of any A.I. construct, the Master Chief was charged with protecting Cortana from the Covenant.

It was around this time that the Chief learned that Covenant forces had successfully captured Keyes and taken him to the Truth and Reconciliation. The Master Chief rescued Keyes, who left to infiltrate what appeared to be a Covenant weapons cache located in a swamp.

The Chief and Cortana used the Silent Cartographer to locate and enter Halo's Control Room, where Cortana was uploaded to Halo's core systems. When the Master Chief asked her how Halo could be used against the Covenant, she hinted that the Halo wasn't what it seemed to be. She also learned that the "weapons cache" Keyes was attacking was really a Flood Containment Facility. She stayed in Halo's systems, sending the Master Chief to find Keyes. After the Chief encountered the parasitic Flood for the first time, he was convinced by the Forerunner Monitor 343 Guilty Spark to activate the Halo. During this time, Cortana apparently absorbed as much data as she could about Halo from its control systems.

343 Guilty Spark helped the Master Chief retrieve the Activation Index. The Chief, intent on using the Index to eliminate the Flood, returned to the Control Room and inserted the Index into the Halo's control panel. Luckily, Cortana stopped the activation sequence and removed the Index's data, informing him of the true purpose of the Halo Array. Cortana's actions saved all life in the galaxy from total annihilation. At that point, 343 Guilty Spark, seeing that the duo had no intention of returning the Index, tried and failed to kill them to retrieve it.

After enduring prolonged engagements with the Covenant and the Flood, Cortana realized that detonating the Pillar of Autumn's fusion reactors would destroy the Halo. Unfortunately, the reactors could only be activated using codes stored in the now-infected Captain Keyes's CNI. The Master Chief retrieved the CNI, and he and Cortana managed to detonate the reactors despite interference from 343 Guilty Spark. The two escaped the resulting explosion in a Longsword fighter.

Dust and Echoes

Cortana and the Master Chief, seemingly the sole survivors of the Battle of Installation 04, discovered a small number of other UNSC personnel that had escaped the ring in a Pelican dropship. Knowing that the Pelican wasn't capable of traveling long distances, the Master Chief, along with Cortana and the Pelican's four-man crew, fought their way onto the Covenant flagship Ascendant Justice. Shortly afterward, Cortana took control of the ship, and returned the survivors to Reach, where the group helped to rescue survivors of the Second Battle of Reach, including her "mother", Dr. Halsey. She managed to improve on the ship's weapons and slipspace capabilities, able to send it to lightspeed below Threshold's atmosphere.

Cortana was revealed to have taken a lot of data from Halo, and the sheer amount of information cut into her processing power and slowed her down. During her time on Ascendant Justice, Cortana exhibited uncharacteristic behavior including anger, distraction, and self-doubt - an indicator that she may have been about to enter rampancy. Dr. Halsey erased some data from her memory to give her more thinking space, including data regarding Sergeant Johnson's immunity to the Flood - a result of Boren's Syndrome.

It was also revealed that during Cortana's time on Ascendant Justice, she had captured a Covenant A.I., decompiling the A.I. and copying two of its functions: the ability to translate Covenant speech, and the ability to create imperfect clones of herself. These capabilities, along with her exclusive knowledge about the Halos, made her extremely valuable to the UNSC.

The Ascendant Justice was effectively fused with the UNSC Gettysburg. It was at this point that Cortana learned of a planned Covenant assault on Earth. The Master Chief, along with SPARTAN Blue Team and an expendable clone of Cortana, would later execute Operation: FIRST STRIKE.

As it turned out, the Covenant A.I. that Cortana had decompiled had managed to, prior to its capture, send a message over Battlenet, warning the Covenant of its ship's capture and sending the necessary calculations for a sub-atmospheric Slipspace jump. The information was later used by the Prophet of Regret to enter Slipspace right above New Mombasa during the Battle of Mombasa.

The Master Chief and Cortana would later return to Earth, at which point Cortana handed all of the sensitive data in her possession over to ONI.

Battle of Earth

Main article: Battle of Earth
Master Chief about to "upload" Cortana into his neural interface.

After returning to Earth, Cortana served on the Orbital Defense Platform Cairo, where a ceremony for both Sgt. Johnson and Miranda Keyes was soon interrupted by the arrival of a Covenant Fleet under the command of the High Prophet of Regret, starting the Battle of Earth. Cortana was given control of the Cairo's Magnetic Accelerator Cannon to repel the invaders, and with the Master Chief's help, she successfully deactivated a Covenant bomb that would have destroyed the station. She did this by uploading to the Master Chief's armor again for the first time since the capture of Ascendant Justice. When she did this, she somehow was able to do it through him merely touching the terminal her hologram was on, possibly an improvement as a result of Master Chief's new MARK VI armor. The same bomb was then used by Spartan-117 to destroy a Covenant Assault Carrier. The Chief offered for her to remain behind on the station after she said that his plan was crazy, but she chose to accompany him again, stating, "Unfortunately for us both, I like crazy." She then aided him when he arrived in New Mombasa to deal with a Scarab.

Delta Halo

Main article: Battle of Installation 05

Later, after escaping on-board the In Amber Clad in a Slipspace event, they discovered another ringworld, Delta Halo. Cortana gave Commander Miranda Keyes access to all information on the original Halo Ring, and provided intelligence to the Chief, UNSC Marines and the ODSTs on the surface of the ring.

After the Master Chief hunted down and killed the Prophet of Regret on Delta Halo, he, Cortana and The Arbiter were captured by the Flood central intelligence - the Gravemind. However, it did not harm them, instead choosing to use the two to stop the Prophet of Truth from firing the Halo. Gravemind sent the Master Chief and Cortana to the Covenant Capital Ship High Charity, where Cortana infiltrated the city's computer systems and remained there while the Master Chief followed the Prophet of Truth. She promised to detonate the crashed In Amber Clad's reactors to destroy the city and Halo if the ring was activated. However, she was left behind as a fail safe because she did not want to chance a remote detonation. As Truth boarded the Forerunner Dreadnought in the heart of the city to reach the Ark, Cortana fought with the ancient Forerunner A.I. Mendicant Bias to prevent the ship from launching without the Chief on board. The firing of Halo was averted by Miranda Keyes, the Arbiter, and Johnson, while the Chief successfully boarded the Dreadnought and escaped High Charity, leaving Cortana in the clutches of the true enemy, Gravemind, who had, by then, overran High Charity.


"Chief...High Charity...the Covenant's Holy on its way to Earth...with an army of Flood."
—Cortana's recording for the Chief.

Under the control of the Gravemind and constantly being tortured, Cortana managed to send a message to the Master Chief on Earth, stashing it on an Earth-bound Flood-infected ship that crash-landed in Voi. In her message, she stated that the Gravemind was approaching Earth in High Charity, and that it was unaware of the portal generated by the Artifact and where it led to. On the other side, there was a solution to stop the Flood without needing to fire the remaining Halo rings; however, she couldn't give any further information, as the Gravemind might have been listening. Though Lord Hood doubted her plan, fearing it could be a Flood trap, the Chief stated that he trusts her. A joint UNSC-Covenant Separatist task force then entered the Portal, heading to Truth and to Cortana's solution. Ironically, Lord Hood was correct: the Gravemind delibrately let Cortana send the message to lure all of its enemies into one place, and then the Flood would overwhelm them all with the infested High Charity.[4]

Cortana continued to appear to the Master Chief, who successfully recovered her from the Flood Hive that was High Charity after it crashed on the Ark. Along the way, the Master Chief had several visions of her seemingly in pain. Surprised that the Chief had against all odds rescued her as he promised after the First Battle of High Charity, as well as being surprised that Chief and Thel 'Vadam (whom she encountered on Delta Halo with the Gravemind) "made nice", Cortana managed to gather herself and produce the Index from Installation 04, which she had kept. With it, Cortana was able to activate the newly constructed Installation 04, which fired prematurely causing it to destroy itself and heavily damage the Ark in the process.

Stranded in Space

"But you did it. Truth and the Covenant...the Flood. It's finished."

The Slipspace portal collapsed as the Master Chief, Thel 'Vadam, and Cortana attempted to escape through it, cutting the UNSC Forward Unto Dawn in half. While 'Vadam, who was on the bridge, managed to return to Earth safely, the Chief and Cortana, who were in the hangar, were left drifting in space. Cortana activated a distress beacon, but knew that it could be years before they were found. As the Master Chief prepared to go into cryogenic sleep to await rescue, Cortana confessed to him that she would miss him.

Five years later, in 2557, she and the Chief are still stranded. Cortana, who is showing signs of disruption or Rampancy, tries to communicate with the Chief. As he is still in cryo sleep, she is unable to get a response from him. Cortana then begins to file a report on the history of the Forerunners and Humanity. After some unknown period of time, they are seen drifting towards an unidentified planet.


Cortana in the Halo 3 instruction manual.

Cortana has a witty and playful personality and a small sense of cryptic humor laced with some sarcasm. She has neither arrogance nor false modesty about her immense capabilities, and her statements about her abilities have an objective perspective that human beings typically cannot achieve, but she does get bored often and easily. In fact it is said that seven seconds of inactivity for an A.I. is excruciating. She has genuine, not merely programmed, loyalty to humanity and the UNSC, but exhibits devotion to John-117 beyond that which her programming or mission requires. She seems to be most loyal to him and is willing to help him with any task he requests of her. After she found out exactly what happened to the Master Chief as a child, she decided to protect him from further harm to the best of her abilities without compromising her mission.

Her personal loyalty is regarded as unwavering, but as an A.I. construct she is subject to corruption. Lord Hood questioned her reliability when it became clear that she had been compromised in some way by the Gravemind's possession of High Charity, on which she was trapped. John-117, however, never questioned her integrity. Cortana did consent to answer some of the Flood's questions, as a strategy for survival and the possibility of gaining information for the UNSC. Her sanity was pushed to the brink as she eluded the Gravemind's attempts to capture and dissect her for information. Before she reunited with John-117 in Halo 3, she sent him a message, telling him about the Ark and warning him of the Flood-infested High Charity's approach to Earth. She was instrumental in finally putting a stop to the Flood at the end of the game.

She frequently jokes about having a relationship with the Master Chief and it is often implied that the two characters have developed some form of attachment. In Halo: The Fall of Reach, she says to Dr. Halsey that the Master Chief is "attractive in a primitive animal sort of way" while examining a photo of him.


Main article: Cortana Moment

Cortana is also very aware of her short lifespan ("Smart" A.I. lifespan is an average of 7 years before rampancy) and her derivative nature as a copy of part of another person, rather than a true human being. Desperate and tortured aboard High Charity she murmurs: "A collection of lies; that's all I am! Stolen thoughts and memories!" Later on she says: "I'm just my mother's shadow..." and "It was the coin's fault," referring to the game of chance that Dr. Halsey played with John-117 when he was young . She, along with Mendicant Bias, is one of only two (known) A.I.s that may have progressed completely through rampancy and became metastable.


As Cortana is an A.I., she has no physical body. She can communicate through comm systems and project a holographic image of herself from appropriate projectors, such as Holotanks. Her chosen avatar appears to be a nude female human (albeit censored by symbols over her body), roughly in her early twenties, with purplish/bluish skin, shoulder length purplish/bluish hair cut shorter at the back, and blue symbols scrolling down her body. In Halo: Fall of Reach, Cortana is said to resemble her creator, Dr. Catherine Halsey as a young woman, with a similar attitude "only unchecked by military and social protocol." When in a different emotional state, Cortana usually changes colors. This was especially noticeable in Halo: Combat Evolved, but less so in Halo 2 and Halo 3. Only in specific instances did she produce the color-changing effect. One instance of this was right before the Master Chief rescued her at the end of her eponymous level.

Bungie took a fair of amount of artistic freedom in the evolution of her appearance throughout the Halo trilogy, noticeably from Halo: Combat Evolved to Halo 2; she has longer hair, a more realistic humanoid figure, a much more feminine appearance and a slightly different shade of purple. In Halo 3, she becomes slightly bluer and again her face, hair, and body are changed to look more feminine and realistic.


Cortana was designed to infiltrate computer systems and she is excellent at the task - she has become so intelligent that she understands Covenant technology far more than her makers. As of early 2553, she has never encountered a Covenant security measure that she wasn't able to bypass. In addition, she is proficient with UNSC military hardware and can run military ships and stations by herself. Indeed, the UNSC's primary use of A.I.s is to oversee targeting of point-defense weaponry used in space battles. For Cortana, this is merely an additional capability. She has helped out in several major battles including Operation: First Strike. She is capable of storing large amounts of data within her holographic appearance, hiding it in the microscopic lines of code that make up her visual form. Even when she is in the Data Crystal Chip, microscopic lines of code are running through the holographic "filling".

Cortana can be transferred among various computer systems. In Halo: Combat Evolved she needed a Data Crystal Chip to move in and out of various networks, including the Master Chief's MJOLNIR armor.[5] In Halo 2, she merely needs to be touching another system to access it; however, this is most likely a product of the Master Chief's upgraded armor. Quite strangely, in Halo 3, she reverted to the data chip; this was probably because the Master Chief's armor was badly damaged during the fall to Earth that it reverted to a back up system, which also explains its different shield. However, there are some differences. Instead of having to be physically "plugged in" to the hologram projector, the Chief can just hold the chip close to it, at which point she "walks" off, later "touching" the chip to return to it -- holographic representations of the data transfer.

She is also very good at planning missions for the Chief, including the destruction of Halo. In Halo: The Flood the Chief comments that he's not sure who's better at blowing things up: him or her. It was also her plan that led to the destruction of all of the Flood that had escaped Installation 05 and saved the galaxy from a further Flood invasion. Apparently she has mission planning routines that help her with this as her clone told the Chief that that copy had only limited mission planning routines and was only able to help the Spartans form basic plans.

Another ability that she developed is a limited teleportation ability on Installation 04. She learned how to teleport on Halo while in its control systems, but as she couldn't access Halo's power grid, she couldn't perform this task very often. She did teleport once with the Master Chief by drawing power from his fusion pack saying that she was sure it wouldn't cause permanent damage to his power pack or shields, but both agreed that this should only be done once. She learned where they needed to go from the Covenant Battlenet and teleported them there although they ended up upside down due to her not getting the coordinates completely right. She has not used this ability since although she could presumably use it on any Halo but would have the same power requirements problem.

Another of her abilities is the ability to clone herself. She got this from a Covenant A.I. she destroyed and dissected. She first tested it by copying her language translation abilities and found it worked great. She also could seem to sense what progress the clone had made as if she retained a connection to it. Later, due to the importance of her getting to Earth due to all of the data she'd collected on Halo, the Flood and Covenant technology, she was forbidden from going on the Master Chief's mission, but she was able to make a clone of her infiltration abilities to give the Chief enough of her capabilities to infiltrate the Covenant command and control station. She claimed that this would not be a complete copy, but she thought that what it was would be enough. The clone had at least some of her personality as well. The clone retained her abilities to hack systems and some limited mission planning routines that allowed her to make basic plans to help the Spartans, but was unable to make the complicated plans that Cortana could come up with. The original clone made a copy of itself into the station's systems to help out and due to being overwhelmed by Covenant security A.I.'s, ended up making hundreds of copies of itself which overwhelmed the system and made accomplishing anything hard for the clones as they began to lose their coherent state, but still could control the system. The original clone was left behind in the reactor system. It was placed there to overload the reactors and never removed once it started the process. All of the clones created on the mission were destroyed when the station blew, but provided an invaluable help to the Spartan team.



  • Cortana is voiced by Jen Taylor, the same actress that voiced Princess Peach in the Mario games, Zoey from Left 4 Dead and Keira Stokes from F.E.A.R. 2: Project Origin.
  • In Halo 3, look for a UNSC mobile computer. Watch the lower-left monitor. After a few seconds, Cortana's face will appear for an instant and then disappear. Two of the easiest ways to see this is to either look at the aforementioned screen in the beginning of Crow's Nest, or at one of the computers in the multiplayer map High Ground.
  • There was going to be an alternate story in Halo: Combat Evolved in which when Master Chief rediscovered Cortana inside the control room, she had become mad with power and wanted to take over Halo and the universe.[6]
  • Originally, Cortana was supposed to have a British accent.[7]This is evidenced by the fact that in Halo: Combat Evolved, Cortana uses several British idioms, such as "sod off!" when addressing 343 Guilty Spark.
  • She was rated as one of the ten most disturbingly sexual game characters by and one of the fifty greatest female video game characters ever by Tom's Games.[8][9]
  • In Halo 3, she repeated lines Dr. Halsey has said before such as "You will be the protector of Earth and all her colonies." which Dr. Halsey says to the 6 year old Spartans in Halo: The Fall Of Reach. Cortana also recites a few lines from the Cortana Letters in Halo 3 in some of her messages and in the announcement trailer. Some of the lines are said in the Cortana moments in the level Cortana.
  • Cortana has been through 7 Notable Battles, again referring back to Bungie's love of the number.
  • It was noted by Dr. Catherine Halsey in the novel Halo: The Fall of Reach that at a certain angle, you could almost see a skeletal structure in Cortana.
  • Cortana has many similarities to the Marathon AI, Leela, such as control over certain functions of ships and other locations in their computer systems.
  • Being a smart A.I., Cortana's operational life span is approximately seven years. However, after she took in all the Forerunner information in Halo's control room, her estimated life span was halved due to the vast task of storing, processing etc. all that information.[10] In addition, this also noticeably decreased her efficiency, albeit temporarily.[11]
  • The name Cortana (also Curtana or Courtain) is a latinised form of the Anglo-French curtein, from Latin curtus meaning "shortened." The name is used for a ceremonial type of sword; according to legend, one such weapon was the sword of Ogier the Dane; it bore the inscription "My name is Cortana, of the same steel and temper as Joyeuse and Durendal." Durendal (spelled 'Durandal' in this sense) was the name of an artificial intelligence in a previous Bungie game, Marathon. This also ties in with Cortana telling the Chief "I am your shield, I am your sword."
  • Strangely enough, although Cortana had worked with the Master Chief a number of times beforehand, Cortana seemed to have been unfamiliar with the Master Chief's armor systems when she was transferred from the Pillar of Autumn into John's MJOLNIR suit. However, due to her tone of voice, she may have been joking.
  • Cortana is the only one to call Master Chief by his real name in the Halo games, at the end of Halo 3.
  • It is unknown how Cortana learned about the Portal and the Ark. In Human Weakness, which takes place directly after Halo 2, she mentions how she can't let the Gravemind know about the Portal or the Ark.


  1. Conversations from the Universe: A transcript involving Cortana is dated "two years prior to events at artifact Halo".
  2. Halo: The Flood, page 255
  3. Axon Clips Chapter 5 Jersey brain_ninjas
  4. Halo: Evolutions, Human Weakness
  5. Halo: The Flood, page 26
  6. Revealed by Jason Jones on the Halo 3 Legendary Edition bonus disk
  7. Revealed by Jason Jones on the Halo 3 Legendary Edition bonus disk
  10. Halo: First Strike page 195
  11. Halo: First Strike



  • The Cortana Letters
Known UNSC AI's
AraquielBeowulfChaunceyCortanaDeep WinterDopplerDurgaDéjàEndless SummerEternal SpringFitzGibbonIonaJerrodJulianaKalmiyaLokiLoreleiLysitheaMackMelissaMo YePallas AthenaRebeccaSerinaSifSolipsilSuperintendent (Vergil) • ToranWellsley

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

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