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. Her first words were "When the game is over, the king and pawn go into the same box" in Italian. 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 ageCortana first met John-117 prior to the Fall of Reach, when she was integrated into his new MJOLNIR Mark V armor. 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.When the operation was canceled due to the Covenant's surprise assault on Reach, the Master Chief was able to fend off Covenant forces at Reach and escaped to the UNSC Pillar of Autumn, while Cortana stayed with Halsey at her excavation site beneath Sword Base. With the Covenant closing in on her lab, Halsey turned Cortana over to the Spartan Noble Team, specifically Noble Six. After fleeing Sword Base moments before it was destroyed, Jun-A266 would escort Halsey to CASTLE Base, while Six, Carter-A259, and Emile-A239 took Cortana to the Aszod Shipyards, where the Autumn was docked.
Although Carter and Emile were both killed by the Covenant's ground forces before making it to the Shipyard, Six would successfully deliver Cortana to Jacob Keyes, the captain of the Autumn, who arrived via Pelican and received "the package". To ensure the Autumn 's escape, Six stayed behind and used a Mass driver to destroy a CCS-class battlecruiser blocking the ship's way out and preparing to glass the shipyard. Six succeeded and ensured the Autumn's safe escape. Cortana reunited with the Master Chief on board.
As soon as Pillar of Autumn escaped the surface and atmosphere of Reach, they jumped into Slipstream Space on a random vector 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 UNSC 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 Command Neural Interface (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 by racing through the ship's crumbling superstructure in a M12-LRV to a hangar bay, where one remaining Longsword fighter was still berthed. Climbing aboard with the Flood right behind them, they barely outran the blast, and watched through the viewports as debris from the reactor breach destroyed the remains of the Halo ring.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 revealed that she had 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 possessed some data on the Halo network including critical information on the Ark.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.
Main article: Battle of Installation 05
Later, after escaping on-board the UNSC 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. 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. 05-032 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.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 succeeded 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 spaceEdit
Cortana, as she appears when the UNSC Forward Unto Dawn begins to detonate.
"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 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 are still stranded. Cortana, who is showing signs of 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 an unknown period of time, they are seen drifting towards an unidentified planet. http://halo.wikia.com/wiki/Cortana