Cortana

"Yank me."

- Cortana to Captain Keyes.

Cortana, UNSC AI serial number CTN 0452-9, is an Artificial Intelligence construct, or "Intelligent Agent". She is a "smart" A.I. (meaning she could perform varying missions, execute tasks and learn new material without having to free up space in her memory having, in essence, a "mind" capable of limitless expansion ), enabling her to perform processes at blinding speeds. She can calculate up to one trillion computations, as well as possessing a personality similar to that of a human. 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 AI for the United Nations Space Command Pillar of Autumn and the Orbital Defense Platform Cairo Station. In addition, she held vital data pertaining to the Halos, such as the Index from Alpha Halo.

Creation
Cortana was created using a flash cloned brain of the famous Dr. Catherine Elizabeth Halsey, the SPARTAN project creator. Twenty of the flash cloned brains were created, but only one survived, which was used to create Cortana. The neural pathways of the cloned brain were scanned and copied through a process called Cognitive Impression Modeling. She is one of the two AI to be 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, and even values. For example, when she was asked by Dr. Halsey to pick a "carrier", Cortana chose John-117 for their neural compatibility, alongside the fact she thought he looked good, with Dr. Halsey agreeing. Being a smart A.I., however, her operational life span is approximately seven years. She is not only a facsimile of Dr. Halsey's brain but also closely resembles her physical form, at a younger age.

Fateful Meeting
Cortana first met the Master Chief prior to the Battle of Reach, where she was integrated into his new Mark V MJOLNIR armor. Together, Cortana and the Chief passed a test that was devised by Colonel James Ackerson. The test included armed ODSTs, 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 black mailed 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.

Discovery
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 but were forced to flee the burning planet, to a randomized set of coordinates 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, they discovered a ring shaped world called "Halo". However, Covenant ships had followed, and began to attack the human ship. Controlling the Pillar of Autumn's defenses, Cortana destroyed four Covenant targets over Installation 04 before the ship's weapons were disabled by Covenant boarders. Per the Cole Protocol, Captain Jacob Keyes, the ship's commanding officer, prepared to abandon ship. Since the protocol forbids the capture or destruction of any A.I. construct, the Master Chief was charged with protecting Cortana from the Covenant. When the Master Chief arrived on Halo, Cortana helms the communications channels and helped to direct Echo-419 and its dropship pilot Foehammer. Human survivors were scattered across the ring and assisted the Master Chief in the rescue of Captain Keyes, who had been captured by Covenant forces and was taken to the cruiser Truth and Reconciliation.

The Master Chief and Cortana then located Halo's Control Room by using the Silent Cartographer. Upon arriving at Halo's Control Room, Cortana was inserted into Halo's core computer and was subsequently flooded by the knowledge of both the Installation and its true threat, asked about how Halo could be used against the Covenant she becomes visibly agitated by the Master Chief's question and partially reveals to him it isn't what he and the others believe it to be. After discovering that what Keyes thinks is a weapons cache isn't what it seems she immediately sends the Master Chief to find Captain Keyes. Cortana stayed in Halo's computer core as the Master Chief encountered the parasitic Flood and was conscripted by the Forerunner Monitor 343 Guilty Spark to activate Halo's defenses.

343 Guilty Spark then teleported the Master Chief to the Library, where he battled more of the Flood with help from 343 Guilty Spark's Sentinels. They then retrieved the Activation Index, the key to activating Halo, and returned to the Control Room. Intent on using the Index, to eliminate the Flood, the Master Chief inserted the Index into the control panel. However, Cortana, who was still inside the control room's core, stopped the activation sequence and took the activation data from the Index. She then surprised Spark by flinging him across the floor. Visibly angry at the Master Chief she informs him of what she had learned: The Halos do not kill the Flood directly, but their food -- humans and Covenant any sentient species alike. If Halo was activated, all life in the galaxy would be annihilated. The Master Chief then questioned Guilty Spark, who confirmed what Cortana had just said. Seeing that the Chief and Cortana had no intention of returning the Index, Spark ordered his Sentinels to kill the Master Chief and retrieve the Index from Cortana.

After avoiding certain doom from the Sentinels and prolonged engagements with both the Covenant and the Flood. Cortana figures that they can destroy the ring by detonating the Pillar of Autumn's fusion reactors, causing an explosion powerful enough to destabilize the ringworld. Unfortunately, the codes are with Captain Keyes. They are able to find the Captain aboard the Truth and Reconciliation however, they both discover the Captain had been absorbed by the Proto-Gravemind, understanding what needed to be done the Chief slams his fist into Keyes skull and retrieves the authorization codes needed to overload the reactors. Chief and Cortana make it back to the Autumn and Cortana successfully starts the detonation sequence, unfortunately Spark stops them, unwilling to be deprived of the wealth of human history. Luckily, the Master Chief managed to detonate the reactors manually before escaping in a Longsword Fighter, just before the ring's destruction.

Dust and Echoes
After the destruction of Halo, Cortana and the Master Chief, seemingly the sole survivors of the tragic events on the ringworld, discovered a small number of other UNSC personnel that had escaped the ring in a Pelican dropship. In order to perform any space travel, the Master Chief, along with Cortana and the four man crew of the Pelican, fought their way onto a Covenant flagship Ascendant Justice. Shortly afterward Cortana took control of the ship, and returned the survivors to Reach and fought the Second Battle of Reach, rescuing survivors from the planet. Ascendant Justice was effectively fused with the UNSC Gettysburg, and she later returned to Earth with the remaining survivors after destroying the Covenant space station Unyielding Hierophant that threatened Earth. Previously, Cortana had captured a Covenant Associated Intelligence present in the Ascendant Justice's computer; it contained a software-replication program. In this instance, Cortana gained the ability to create imperfect clones of her program. along with the ability properly translate Covenant Dialect. The Master Chief and Spartan Blue Team brought one of these clones to the Unyielding Hierophant. This clone then re-cloned itself hundreds of times, making matters difficult. However, the clone managed to secure Blue Team a safe way out of the space station before it was destroyed. It was during this mission that Cortana figured out that Covenant ships could enter Slipspace from within the atmosphere of a planet. This data was stolen by a Covenant A.I. and broadcast to another Covenant ship. This is how the Prophet of Regret was able to enter Slipspace right above New Mombasa during the Battle of New Mombassa. Cortana was revealed to have taken a lot of data from Halo and the sheer amount cut into her processing power and slowed her down somewhat. During her time on Ascendant Justice Cortana exhibits several cases of uncharacteristic behavior including anger, distraction and self doubt, some to such an extent that Cortana even doubts her own capacity to complete her mission. Although she is not rampant, her fragile emotional state is likely an early indicator. The reason that she ended up having to use a clone of herself on the massive refit and repair station Unyielding Heirophant was because the data she collected on Halo, the Flood and Covenant technology made her far too valuable to risk sending her into enemy hands, as all of the information she'd learned was vital and had to get back to Earth. There was nowhere safe enough for her to store said data hence the copies were needed to carry out the mission aboard the Covenant vessel. Once they reached Earth, she turned all of the data over to ONI.

First Battle of Earth
After returning to Earth, Cortana served on the Orbital MAC defense platform Cairo, a ceremony for both Sgt. Johnson and Miranda Keyes, is soon interrupted by the arrival of the Covenant Fleet under the command of the High Prophet of Regret. Cortana was given control of the Cairo's Magnetic Accelerator Cannon to repel the invaders, and with the Master Chief's help successfully deactivated a bomb that would have destroyed the station. 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 remain with him and help 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
""On Halo, you tried to kill Cortana...you tried to kill me.""

- Master Chief to Guilty Spark 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 along with Cortana were captured by the Flood central intelligence, The Gravemind. However, it did not harm them, instead it wanted to use the Master Chief and Cortana to stop the Prophet of Truth from firing the ring. Gravemind sent the Master Chief and Cortana to the Covenant Holy City of High Charity, 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.

Captured
"Chief...High Charity...the Covenant's Holy City...is on it's 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, through a Flood-infected ship. In her message, she stated that the Gravemind was approaching Earth in High Charity but was unaware of the Portal and where it lead to. On the other side was a solution to stop the Flood without needing to fire the remaining Halo rings but couldn't elaborate more, as the Gravemind would also know. Though Lord Hood doubted her plan, fearing it could be a Flood trap, the Chief states that he trusts her. A joint UNSC-Covenant Separatist task force then moves through the Portal to Truth and Cortana's solution.

Cortana continued to appear to the Master Chief, who successfully recovered her from the Flood Hive that was High Charity. 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 Thel 'Vadam and Chief "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 and destroyed itself The Ark along with it.

End of Halo 3
"But you did it. Truth and the Covenant...the Flood. It's finished."

- Cortana

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 days, years even, before they were found. As the Master Chief prepared to go into a cryogenic sleep to await rescue, Cortana confessed to him that she would miss him. They were last seen drifting towards an unidentifiable object.

"I'll miss you."

- Cortana

Personality


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 AI 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 is pushed to the brink as she eludes the Gravemind's attempts to capture and dissect her for information. Before she reunites with John-117 in Halo 3, she sends him a message, telling him about The Ark and warning him of Flood-infested High Charity's approach to Earth. She is furthermore instrumental in finally putting a stop to the Flood at the end of the game.

Cortana is also very aware of her short lifespan ("Smart" AI 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 the young John.

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.

Appearance
As Cortana is an AI, 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 nude (albeit slightly censored by symbols over her body), about in her early twenties, female human with purplish/bluish skin, shoulder length purplish/bluish hair cut shorter at the back, and blue symbols scrolling down her body. 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. 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."

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 figure, making her more human, a much more feminine figure and a slightly different shade of purple. In Halo 3, she becomes slightly bluer and again her face, hair, and body become more womanly and realistic. Her change in "Hair" styling between Halo CE and Halo 2 mirrors Commander Keyes' hairstyle in Halo 2.

Abilities
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 its makers. So far, she has not encountered a security program she was not able to defeat, as she says in Halo 2 while inside High Charity's computer system, "You wouldn't believe the number of kill systems the Covenant are throwing down around me. It's pretty sloppy stuff, though. I guess they never expected a hostile intelligence to penetrate their system from the inside.". 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 AIs 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 such large amounts of data with the many lines of code streaming through her holographic 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. 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 and reverted to a back up system; this is also why the shield is different. However, there are some differences. Instead of having to be physically "plugged in" to the hologram projector, the Chief just holds the chip close to it and she "walks" off and she "touches" the chip to return, holographic representations of the data transfer.

She is also very good at planning missions for the Chief such as 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 much. 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 AI 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 AI'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.

Trivia

 * 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.
 * There are 7 letters in Cortana's name.
 * 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.
 * Originally, Cortana was supposed to have a British accent. This may have been taken over for Serina.
 * She was rated as one of the ten most disturbingly sexual game characters by Games.net and one of the fifty greatest female video game characters ever by Tom's Games.
 * 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.
 * On the level The Covenant, when you just enter the Citadel, when Cortana emerges as a flashback, you can also see her on the screens around you.