Cortana

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"They let me pick, did I ever tell you that?...Choose whichever Spartan I wanted."- Cortana

Cortana, UNSC AI serial number CTN 0452-9, is an Artificial Intelligence construct. She is a "smart" A.I. (meaning she could perform varying missions and options and can learn new material without having to free up space in her memory), capable of performing 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. She is one of the two AI to be created from Dr. Halsey's brain, the other being her predecessor, Kalmiya (also a smart AI). Cortana seems to share her creator's memories, thoughts and even values. An example being that when she was asked by Dr. Catherine Halsey to pick a 'carrier', Cortana had chosen John-117 for their neural patterns compatibility and, with Dr. Halsey agreeing (and it is mentioned that Cortana quoted "You had something that no one else had...luck".) She is modelled after Dr. Halsey when younger. Being a smart A.I., however, her operational life span is approximately 7 years. She is not only a facsimile and dubious dummy of Dr. Halsey's brain but also 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 armour. 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 air strike at the Pillars of Loki. After the test, Cortana was installed into the Pillar of Autumn for the mission she was created for.

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. She had a chance to pick which Spartan she would partner up with and assist. The Spartan she picked was John-117 because of his "luck". It should also be noted that she could have picked John-117 because Dr. Catherine Halsey had always favoured John. In fact, since Cortana thought John "handsome in a primitive, animal sort of way", it is probably what Halsey reflected, as Cortana was simply Halsey's clone.

Discovery
When the operation was cancelled due to the surprise assault on Reach, she and her new partner, John-117, witnessed the death of all the Spartans and were left to flee the burning planet to a randomised set of coordinates per the Cole Protocol. John-117 thought the coordinates were strangely familiar; Cortana scanned them and found that the coordinates matched the symbols on a rock that Master Chief discovered on Sigma Octanus IV and the Covenant ship John-117 had boarded in 2525. After emerging out of slipspace, they discovered a ring shaped world that was promptly named "Halo". However, Covenant ships had followed, and began an assault. Controlling the Pillar of Autumn's defences, 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 Foehammer, a dropship pilot, to human survivors scattered across the ring and assisted the Master Chief in the rescue of Captain Keyes from the Covenant ship 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 looked for a way to activate Halo to use it as a weapon against the Covenant, but became visibly agitated and sent 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 a Forerunner construct named 343 Guilty Spark to activate Halo's defences.

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, the key to Halo, to eliminate the Flood, the Master Chief inserted the Index into the control panel where Cortana who revealed the truth that she stopped him had learned: The Halos do not kill Flood, but their food. If Halo was activated, all sentient life (a.k.a. anything that could think) in the galaxy would be annihilated. She took the Index and thus became a target for 343 Guilty Spark. Having captured the Index, Cortana and the Master Chief planned to destroy Halo. They succeeded after Cortana helped the Chief detonate the  Pillar of Autumn's fusion reactors, causing an explosion powerful enough to destabilize the ringworld. The two escaped in a Longsword Fighter and witnessed the ring's destruction.

Dust and Echoes
""Scanning...just dust and echoes. we're all that's left. We did what we had to do—for Earth. An entire Covenant armada obliterated. And the Flood-we had no choice. Halo-it's finished.""

- Cortana

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 a damaged Covenant flagship, Ascendant Justice, and returned the survivors to Reach and fought the Second Battle of Reach, rescuing survivors from the glassing of 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. (This is also the first time Cortana encountered the Brute species.) 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. The Master Chief and Spartan Blue Team brought one of these clones to Unyielding Hierophant. This clone then re-cloned itself hundreds of times, making matters a little difficult. However the clone managed to secure Blue Team a safe way out of the space station. 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 why the Prophet of Regret was able to enter slipspace right above New Mombasa during the First Battle of Earth.

First Battle of Earth
""I've been analyzing the Covenant tactical chatter. They're surprised, confused... I don't think they expected us to be here. Not... you and me...all of us... humanity, on Earth. Odd, I know, but it does help explain why they came here with such a small fleet.""

- Cortana

Returning to Earth, Cortana served on the Earth defence platform Cairo during the awards ceremony for the survivors of the first Halo installation. When a Covenant Fleet under the command of the High Prophet of Regret arrived, Cortana took control of the Cairo's Magnetic Accelerator Cannon (or MAC gun) 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.

Delta Halo
""That...is another Halo""

- Cortana

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 ODST's on the surface of the ring.

After the Master Chief assassinated the Prophet of Regret on Delta Halo, he along with Cortana were captured by the Flood leader, the Gravemind. However, the Gravemind did not harm them, instead it wanted the Master Chief and Cortana to stop the Prophet of Truth from firing the ring. The 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. The firing of Halo was averted by Keyes, the Arbiter, and Sergeant Major Avery Johnson, while the Chief successfully boarded the Dreadnought and escaped High Charity, leaving Cortana in the clutches of the ally turned enemy, the Gravemind, who had, by then, overrun High Charity, by choice.

Captured
""Chief...High Charity...the Covenant's Holy City...is on it's way to Earth...with an army of Flood.""

- Cortana

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 opened by a Forerunner artifact on Earth. 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, although it is unknown how a program could feel this. Surprised that the Chief had against all odds rescued her (as he promised after the First Battle of High Charity), Cortana produced the Index from Installation 04, which she had kept as a souvenir. With it, Cortana was able to activate the newly constructed ringworld. The new Installation 04, was fired prematurely and destroyed itself, and The Ark along with it.

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

- Cortana

While the Flood were destroyed as planned, the slipspace portal collapsed as the Master Chief, the Arbiter and Cortana attempted to escape through it, cutting the UNSC Forward Unto Dawn in half. While the Arbiter (who was on the bridge) escaped to Earth through the portal, 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 a cryogenic sleep to await rescue, Cortana confided to him that she would miss him. He replied to wake him when she needed him.

Personality


Cortana has a witty personality and a small sense of 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.

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 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 naked, about in her early twenties, female human with purplish/bluish skin, short red hair, and blue to green symbols scrolling down her body. In cases of being 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 Cortana moment occurred 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.

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 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 armour. 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 armour. Quite strangely, in Halo 3, she reverted to the data chip, this was probably because the Master Chief's armour 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.

Also Cortana seems to have an ability exclusive to herself and 343 Guilty Spark (she may have gained it while in Halo's core). This ability is being able to hold actual solid objects (such as the Index) even though she is a merely a holographic form that should logistically not be able to hold solid objects. Although this may be possible if Cortana's image is displayed with light similar to Light Bridges.

Trivia

 * Since the first Halo game Cortana's color changes. In Halo: CE, she was a violet/deep plum color, Halo 2 a blue/violet and Halo 3 a light shade of blue.
 * Cortana is voiced by Jen Taylor, the same actress that voiced Princess Peach in the Mario games.
 * In Halo 3, look for one of the UNSC mobile computers. 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 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.
 * Cortana's hair, body and face get more realistic as each new Halo game gets updated.
 * 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 Cortana Level.
 * Cortana is cloned from Dr. Halsey's brain and Halsey was very close and attached to Master Chief, which is a possibility why Cortana is also very attached to Master Chief and it is possible her face is most likely similar to or the same as Dr. Halsey's.
 * In Halo 2, through modding, it can be found she has animations for some guns, although they are very simplistic variations of her standard pose.
 * Cortana has been through 7 Notable Battles, again referring back to Bungie's love of the number.
 * In Halo 2 and Halo 3, Cortana and Miranda Keyes have a similar hairstyle, a shoulder length crop.
 * "Smart" A.I. such as Cortana live for up to 7 years, another Bungie 7 reference.
 * 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's quote "I keep what I steal," is possibly referring to the Index that she keeps through the entire Halo series.
 * In Halo: Combat Evolved, Cortana has a different color scheme of green and yellow to red and blue.
 * Cortana resembles Jane in the Enders Game book series.
 * In Halo 2, even though she's only a program, when she shows up (i.e. the Level Gravemind on the holopanels), if you shoot her, the shots will not go through her; rather, they will disintegrate upon hitting her.
 * Cortana has many similarities to the Marathon games' AI, Leela, such as control over certain functions of ships and other locations if in their computer systems.
 * When Cortana is inside the Master Chief's armor, she seems to be able to see and possibly hear what he (the Master Chief) sees and hears. This is suggested in Halo: Combat Evolved on the level Assault on the Control Room when she says "That terminal; try there", and when at the end of Halo: Combat Evolved, she says, "Spare me a look?" and John walks over to the window to look at the just-destroyed Halo Installation 04.
 * Halo 3 was the only game in the series that had Cortana in every single Campaign level. In Halo: CE, Master Chief had to leave her at the Control Room, and in Halo 2, the story line switches between Arbiter and the Chief. However, she has only appeared in the first levels through messages sent to the Chief.
 * Quotes spoken by Cortana in Halo 3 before you rescue her are possibly Dr. Halsey's thoughts/memories, "Do you like to play games? So do I.", possibly referring to when in the first book, "Fall of Reach", Dr. Halsey met John after observing him for a period of time. She flipped a quarter, he guessed right, then he got to keep it.