Cortana

"This Galaxy is vast; its wonders and beauty are almost unfathomable. But the galaxy also hides dark secrets, some of which have lain dormant since the beginning of time itself. There is a danger in secrets, both in seeking and in knowing. Some things are meant to be hidden from view. Some mysteries defy understanding, and sometimes even the things we think we know are untrue. Some secrets should remain untouched."

- Cortana

Cortana, UNSC Artificial Intelligence serial number CTN 0452-9, is a "smart" A.I. construct. 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 Pillar of Autumn, the Orbital Defense Platform Cairo Station and the UNSC frigate In Amber Clad. In addition, she held vital data pertaining to the Halos, including the Activation Index from Installation 04.

Creation
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 a small number proved viable candidates for A.I. creation. One of these would be used to create Cortana, and another would be used for her "sister" AI Kalmiya. The neural pathways of the cloned brain were scanned and copied through a process called Cognitive Impression Modeling. After her creation, Cortana's first words were "When the game is over, the king and pawn go into the same box" in Italian.

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 her avatar is also a replica of her physical form, albeit at a younger age.

Fateful meeting
Cortana first met John-117 prior to the Fall of Reach, when she was integrated into his new MJOLNIR Mark V armor. This marked the first time an AI had been integrated with a human brain via a neural interface. Together, Cortana and the Chief passed a test that was devised (Dr. Halsey would have called it "sabotaged") 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 to run the ship's shakedown and oversee the refit. Afterward it was planned that she would be replaced with the Pillar of Autumn's true AI, but she was forced to take up this duty herself ultimately. 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. She also developed a deep personal loyalty to John-117 that would only grow stronger over their adventures together.

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 Fall of Reach
At some point before the Battle of Reach, Dr. Halsey separated Cortana into two "fragments". One of these fragments, which contained all of her higher functions and personality, was stationed on board the UNSC Pillar of Autumn, while the other was tasked with mining data from the Forerunner artifact beneath Sword Base. When the Covenant began to glass the planet, Halsey tasked Noble Team with bringing Cortana's fragment to the Pillar of Autumn. Afterward, the two halves were reunited, and Cortana was able to use the data collected from the artifact.

The 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 Pillar of Autumn's crew after 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 Raid 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 (with all of the data the real Cortana had she was just too valuable to risk), 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 although she held onto the Index and apparently still possesed some data on the Halo network including critical information on the Ark.

Battle of Earth


After returning to Earth, Cortana served on the Orbital Defense Platform Cairo, where a ceremony for both Sgt. Johnson and Commander 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 anyway. She then aided him when he arrived in New Mombasa to deal with a Scarab.

Delta Halo
Later, after escaping on-board the In Amber Clad in a Slipspace event, they discovered another ringworld, Delta Halo. Cortana gave Miranda Keyes access to all information on the previous 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. The 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 Thel 'Vadamee, 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, overrun High Charity.

Captured
"Chief! High Charity, the Covenant's Holy City is 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. She succeded in doing this by creating a message and using the Gravemind's link to that ship to transmit it. The Gravemind allowed this and even helped it along in order to lure the Master Chief in, but was unaware of what the message said. 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 deliberately 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. It was also shown that some of the Cortana Moments were of her defying the Gravemind and some were clones of her that she made to distract the Gravemind to avoid being consumed by him.

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. While the Chief reassured her, Cortana knew that she had taken irreparable damage in some places. 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."

- Cortana

The Slipspace portal collapsed as the Master Chief, Thel 'Vadam, and Cortana attempted to escape through it, cutting the 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.

Four years later after the portal collapse in 2552, the year 2556, she and the Chief were still stranded. Cortana, who was showing signs of Rampancy, tried to communicate with the Chief. As he was still in cryo sleep, she was unable to get a response from him. Cortana then began to file a report on the history of the Forerunners and humanity. After an unknown period of time, they are seen drifting towards an unidentified planet.

Personality
Cortana has a witty and playful personality, and what has been described as a "snarky" sense of sarcastic humor. 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. Her loyalty is first and foremost to humanity and the UNSC, but she exhibits devotion to John-117 beyond that which her programming or mission requires. After she learned of the events endured by John during the SPARTAN-II conscription process, she decided to protect him from further harm to the best of her abilities without compromising her mission.

Cortana's 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. Her personal loyalty to and unwavering trust in John-117 helped anchor her and allow her to hold on despite being driven to the point of rampancy. Before she reunited with John-117, 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 during the events that followed.

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 romantic 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. In Halo 3 his mere presence and reminder of his promise to her are enough for her to pull herself together to help him.

Rampancy
Cortana is very aware of her short lifespan (a "Smart" A.I's lifespan is an average of seven 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. Halo: Evolutions Human Weakness reveals some of this to be her defying the Gravemind and a few of the more rampant things she says to be copies she made of herself which have been consumed by the Gravemind. She, along with Mendicant Bias, is one of only two known A.I.s that may have progressed completely through rampancy and became metastable.

However, this theory of metastability may have been disproved in the Halo Legends short film Origins, in which four years after the events of Halo 3, it is strongly suggested that Cortana is falling into rampancy. She displays several characteristics to support this, such as her hologram flickering and trying to communicate with John-117 despite him being in cryo-sleep. She even tried to make physical contact with John via her avatar. Cortana's fate is, as in the game, left ambiguous.

Appearance
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 John-117 rescued her. Dr. Halsey stated in her journal that Cortana looks somewhat like Miranda Keyes.

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.

Abilities
Cortana is an extremely advanced "Smart" AI, described once as "a generational leap" in AI technology. Her software is designed to infiltrate computer systems, and she is excellent at the task - as of early 2553, she had 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 almost entirely by herself. The UNSC's primary use of AIs is to oversee targeting of point-defense weaponry used in space battles, but for Cortana, this is merely an additional capability.Cortana has acted as the AI of the Pillar of Autumn, Cairo Station, the Forward Unto Dawn, the Gettysburg and even the Covenant flagship Ascendant Justice.

Cortana can be transferred among various computer systems, either through a data crystal chip or through close physical proximity to a computer system (though it appears that the method of transfer depends on the available technology).

On the battlefield, Cortana is able to gather data from local sources (including the Covenant Battlenet) and improvise effective battle strategies. John-117 acknowledged her as providing "intel support in an operation where their had been no reconnaissance." Her efficiency for planning has helped John-117 and others in many dire situations.

Cortana is also capable of interfacing with Forerunner technology. During the Battle of Reach, she was able to decode a large amount of data from the Babd Catha Forerunner Complex, and while on Installation 04 she was able to make use of the installation's Teleportation Grid.

Another of her abilities is the ability to clone herself, which she learned from a Covenant A.I. she captured and dissected. She can create multiple runtimes of herself to carry out different tasks simultaneously. At one point, she created a clone of her infiltration abilities to give the Chief enough of her capabilities to infiltrate the Covenant command and control station. Although not a complete copy, the clone had at least some of her personality. 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. All of the clones created on the mission were destroyed when the station blew, but provided an invaluable help to the Spartan team. Later, while held captive by the Gravemind, Cortana used her cloning ability to create data-stripped clones of herself and ones of her lower-priority functions to distract the Gravemind. These were all consumed by the Gravemind, but they helped buy Cortana time and one also helped her create her message to the Master Chief. Some were even responsible for the more rampant parts of two of the Cortana Moments.

Cortana is capable of linking her consciousness with a SPARTAN-II through the SPARTAN's armor and neural interface, allowing her to enhance the performance of the armor and communicate directly to the SPARTAN's mind. She has displayed this capability extensively during her time serving with John-117. Although this is not necessarily an ability exclusive to Cortana, her neural link with John-117 marked the first time that a "Smart" AI had joined minds with a human (as noted by the Assembly in 2552).

Trivia

 * Cortana is voiced by Jen Taylor, the same actress that voiced Princess Peach in several Mario games, Zoey from Left 4 Dead, Keira Stokes from F.E.A.R. 2: Project Origin, and also voices Catherine Halsey, reinforcing the connection between the two characters. This is also the case in Halo Legends, where Shelley Calene-Black voices both Halsey and Cortana.
 * Easter eggs involving Cortana can be found in a couple places. 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.
 * In the original draft of the Halo: Combat Evolved script, Cortana was supposed to have a British accent. When in search of voice actors, Martin O'Donnell made sure they had the ability to interpret the accent correctly 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 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 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 possibly halved, due to the vast task of storing, processing etc. all that information. In addition, all of the data she absorbed on Halo noticeably decreased her efficiency. On the other hand, it has been suggested that Cortana found a way to use that information to prevent her own "death" from Rampancy, remaining stable when normal AIs would have shut down.
 * 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." The alternate spelling "Durandal" was used as 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."
 * The Chief appears to be unaware that Cortana is created from Dr. Halsey's cloned brain, although he can recognize that whoever died to create the A.I must have been a genius, and that Cortana sounds more like a picky civilian than a military construct.
 * Her first words were, "Quando il gioco è finito, il re e il pedone vanno nella stessa scatola." This phrase translates to "When the game is over, the king and the pawn go in the same box." The phrase was spoken by Halsey's mother after their first game of chess.
 * Cortana's voice is available in Halo: Reach's Firefight mode.