Cortana (Earth-4001)

Cortana (AI Serial Number: CTN 0452-9) is a "smart" A.I. formerly in service with the United Nations Space Command. Unique and exceptionally powerful even among smart A.I.s, she was one of the most important figures in the Human-Covenant War, and served as John-117's partner in the final months of the conflict. Her flexibility and tactical skill proved invaluable in boosting the combat ability of the Halcyon-class light cruiser Pillar of Autumn, the orbital defense platform Cairo Station and the Stalwart-class light frigate In Amber Clad. In addition, she held vital data pertaining to the Halo Array, including the activation index from Installation 04.

Personality & Traits
Cortana has a witty and playful personality, with a sarcastic sense of humor. While she is not boastful, she does take pride in her adaptability as an A.I., and occasionally teases John-117 about her invaluable talents.

Cortana's personal loyalty is regarded as unwavering, but as an AI construct she is subject to corruption and rampancy. Near the close of the Human-Covenant War, she was captured by the Flood Gravemind on High Charity, and was continually assaulted and interrogated by the Gravemind. Her stability was pushed to the brink as she eluded the Gravemind's attempts to capture and dissect her for information. Among the Gravemind's favorite tactics were exploiting Cortana's insatiable desire for knowledge, the nature of her artificial existence, and providing her glimpses of thoughts and feelings from humans absorbed into the Flood collective. In order to preserve herself from destruction and possibly gain information for the UNSC, she eventually consented to give up some pieces of information to the Gravemind. Her personal loyalty to and unwavering trust in John-117 helped anchor her and allow her to hold on to her sanity. She was instrumental in finally putting a stop to the Flood during the events that followed.

Cortana seems to share some of her creator's memories, thoughts, and opinions. 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. However, Cortana was torn over the morality of the SPARTAN-II project, vowing to protect John-117 from any future threats. This was decisively demonstrated when Cortana set out to ruin the career and reputation of Colonel James Ackerson for his attempted killing of John during a training exercise.

Relationship with John-117
While her loyalty was initially first and foremost to humanity and the UNSC, Cortana exhibited a unique devotion to John-117 beyond that which her programming or mission requires and eventually ended up feeling more loyal towards him. 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.

She frequently joked with the Master Chief, and has found some of his inquiries amusing in the way an older sister does a "naive baby brother". She stated to Dr. Halsey that the Master Chief is "attractive in a primitive animal sort of way" while examining a photo of him. After John rescued her from High Charity, his mere presence and reminder of his promise to rescue her are enough for Cortana to pull herself together to help him. She was, as classified by the AI constructs of the Assembly, "re-made as one" with her creators.

Abilities
Despite being based upon third-generation "smart" A.I. architecture (which was already succeeded by two newer generations at the time of her creation), Cortana is an extremely advanced A.I., described once as "a generational leap" in A.I. technology. Her software is designed to infiltrate computer systems, and she is excellent at the task - as of 2552, she had never encountered a Covenant security measure that she was not able to bypass. In addition, she is proficient with UNSC military hardware and can run both warships and stations entirely by herself. The UNSC's primary use of A.I.s in combat is to oversee targeting of point-defense weaponry used in space battles, but for Cortana, this is merely an additional capability. Much more efficient than a human crew, she can greatly boost the combat capability of a vessel; while operating UNSC Pillar of Autumn, she was able to defeat four CCS-class battlecruisers out of a dozen, a feat normally unheard of for a human ship. Cortana has acted as the A.I. of the UNSC Pillar of Autumn, Cairo Station, the UNSC Forward Unto Dawn, the UNSC Gettysburg, and the Covenant flagship Ascendant Justice.

Cortana can be transferred among various computer systems, either through a data crystal chip or simply through close physical proximity to a computer system (though it appears that the method of transfer depends on the sophistication of 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 value of providing "intel support in an operation where there had been no reconnaissance." Her efficiency for planning has helped John-117 and others in many life or death situations.

Cortana is also capable of interfacing with Forerunner technology. During the Fall 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.

One of Cortana's most unique abilities is her ability to create "clones" of 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, and can control the level of intelligence and the number of abilities of each clone. Cortana once created a clone of herself that contained copies of her decryption and translation software, and set it to interface with a Forerunner data terminal on Reach. Later, she was reunited with this copy, and assimilated the information that it had gathered. She and Halsey were able to achieve a similar feat through a "Solomonic solution", which instead divided her into individual copies, rather than cloning. Cortana was able to create a clone to help with Operation: FIRST STRIKE; this clone ultimately made more clones that multiplied into numbers in the hundreds.

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. Doing so is described as "cold mercury" seeping through the Spartan's brain, and brings their reaction time to near-instanteous limits, though she cannot block thoughts or force control of the Spartan's body. 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).

Description
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 is a nude female human (albeit censored by geometric patterns over her body), roughly in her early twenties. She appears with purple/blue skin, shoulder length purple/blue 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 when she was embedded in the Core of Installation 04's control center.

Cortana has been said to resemble her creator, Doctor Catherine Halsey as a young woman, with a similar attitude "only unchecked by military and social protocol." Dr. Halsey stated in her journal that Cortana looks somewhat like her own daughter, Miranda Keyes.

Trivia

 * "Cortana" (more commonly rendered as "Curtana") is the legendary sword of Ogier the Dane, which is said to bear the inscription, "My name is Cortana, of the same steel and temper as Joyeuse and Durendal."
 * Cortana's creation date, November 7, is a reference to John-117's service tag, as the date can be written 11/7. The year of her creation is a reference to the number seven, as 2+5=7 and 49=72.