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Cortana, as she appears in Halo 3

Cortana, UNSC AI serial number CTN 0452-9, is an Artificial intelligence construct.


Cortana is a smart A.I., meaning she has the ability to perform processes at blinding speed like a normal AI, but also making her capable of assuming a personality akin to a human civilian. She is a "smart" artificial intelligence, but the drawback is she will over think herself to death once her seven years are up. She is the artificial intelligence behind the Pillar of Autumn, although she does not have absolute control; Captain Keyes retains some exclusive powers, which he can execute through his neural implants. This is likely used as a failsafe should rampancy ever occur.

Cortana has no physical body, but she can communicate through comm systems and project a holographic image of herself from appropriate projectors, such as Holotanks. Her chosen avatar is that of a female human with purplish skin, short hair, and blue to green symbols scrolling down her body. Her appearance changes noticeably from Halo: Combat Evolved to Halo 2; she has longer hair, a more realistic figure, making her more human, a more feminine figure, and a slightly different shade of purple.

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.[1] 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, but 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.

Cortana was designed to infiltrate computer systems and she is very good at that task. She has become so intelligent that she understands Covenant technology more than it's makers. So far, she has not encountered a security program she was not able to defeat. In addition, she is proficient with UNSC military hardware and can run military ships or 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.

Cortana was actually created using a cloned brain of Dr. Catherine Halsey, the SPARTAN project creator. It is mentioned in Halo: Fall of Reach that she resembles a younger Dr. Catherine Halsey, with a similar attitude ‘only unchecked by military and social protocol’. Cortana's primary mission was to assist the SPARTANs in their mission to capture a Covenant Prophet and return him to Reach for interrogation.

Cortana has a smart, witty personality and a good sense of humor. She has hardwired loyalty to humanity and the UNSC but seems to be genuinely loyal in any case. Her loyalty was brought into question after the events of Halo 2, where she accepts (but somewhat aggressively) to answer the Gravemind's questions. When she is reacquainted with the Master Chief in Halo 3, she admits to answering his questions and regrets it, and proves her loyalty by helping the Master Chief to contain the Flood.

Cortana and the Spartans[]

One of her primary missions was to assist the Spartans in the capture of the Covenant High Prophets, and then to negotiate either a truce or peace treaty.

Cortana has no physical form, unlike 343 Guilty Spark's avatar. However, she maintains the ability to communicate a strong female voice through available communications systems and, if possible, project a holographic image of herself. Originally, the core of Cortana was contained in a disk which could be inserted into most systems; however, the MJOLNIR Mark VI armor system is apparently equipped to allow her to transfer from system to system with a mere touch of the palm. Cortana was designed to infiltrate any security system, and once she is physically inside, there is little that can stop her from taking absolute control.

Cortana was made to share the SPARTANS' MJOLNIR suits. Later the Master Chief is set to escape with her from the attacked ship Pillar of Autumn, guiding him through his various mission tasks on Halo. Master Chief's reaction speed is greatly increased by this, as Cortana resides in the space between his mind and his suit and further boosts his already superhuman reaction speed.

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 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.

Cortana and Rampancy[]

Cortana displays many signs of oncoming rampancy. Whether these symptoms are transient and can be ignored, her programming (being part of the Halo universe and not the similar but distinct Marathon universe) allows for these, or she is actually becoming rampant for good or evil, is the topic for considerable debate. Several instances of potential rampancy are discussed below; these are classified as such by the definition of rampancy derived from the Marathon universe.

Rampancy in Halo: Combat Evolved[]

Fans have speculated that Cortana begins showing signs of rampancy late in the game. During the course of the game, Cortana spends 12 hours in Installation 04's core computer. When first merged with the core she shows signs of uncontrollable knowledge and is unable to focus on the task at hand. When the Chief asks her questions, she becomes irritable and aggressive to his questions. Under the Marathon definition of rampancy, this outside stimuli combined with what is assumed to be an extremely large network would allow a rampant AI ample opportunity for growth. And to support this theory John mentioned in the book, Halo: The Flood that she did seem to take up more space. This is either a sign of rampancy or the fact that she has the combined knowledge of the Forerunners and the Index. Another theory is that Cortana's contact with the Halo's systems made her realize what small significance she had in the universe, as opposed to other systems; something similar to what the AI Durandal went through in Marathon. To this end, she may be trying to achieve more power by trying to attempt something related to the halos. Her holographic color has also changed from purple to green with orange eyes instead of blue.

Rampancy in Halo 2[]

There is circumstantial evidence in Halo 2 which suggests that Cortana is in the stages of rampancy.

As the Arbiter and Miranda Keyes are attempting to disengage Delta Halo by removing the Index, Cortana is on High Charity in a position to detonate the ship and destroy the Covenant city and Delta Halo in a chain reaction. Cortana does not do this, even though Miranda's effort to pull the Index out of the energy stream was done apparently in the nick of time.

A small cinematic sequence after the credits at the end of Halo 2 shows Cortana conversing with the Gravemind creature, who is presumed to be the controlling intelligence behind the Flood. When it says it has questions, she says, "All right, shoot." However, Cortana says this in a fairly aggressive way. Considering the nature of the Flood, her actions seem extraordinary and very difficult to interpret. However, rampant AIs typically concoct plans which are surprisingly beneficial to those who think the plan will doom them. Cortana's ever-growing abilities may enable her to remain loyal to the intent of the UNSC -- to protect humanity -- while seeming to disobey their direct orders by allying herself with the "enemy."

A last possible hint of rampancy is a quote Cortana says in the game level, Delta Halo. As soon as the first Pelican comes in for support with a Warthog, Sergeant Johnson states that he can see a view of a building in the middle of a lake. Cortana replies, "Yeah, I saw it too. It looked like a temple. If I were a megalomaniac, and I'm not, that's where I'd be." One could say that she quickly defended herself from her own statement, leading one to believe that she may soon be viewed as a rampant AI, however it is most likely just a humorous statement aimed at any opinion the player and/or Master Chief may have formed about her personality, similar to the jokes between her and the Chief in Halo: The Flood.

Rampancy in Halo 3[]

Cortana has been quoted as saying, "No more sadness, no more anger, no more envy!" in one of her cryptic flashes in Halo 3. These are the three stages of rampancy from Marathon. She has been heard crying and laughing. One theory is that part of Cortana was corrupted by Gravemind; this part became Rampant, and helped him. The other part became his slave, and is the part the Chief rescued. The theory that Cortana had been split in multiple personalities comes from her everchanging attitude from the flashes; one second she is taunting the Chief, the next she acts as if she doesn't know who he is, the next she is trying to warn him. She may have split herself up purposely, as she did in First Strike. She could have given Gravemind a part of her to use, to try and maybe trick him.

Another theory is that the Gravemind impersonated Cortana during several flashes, such as the last one before the Master Chief found her, she appeared and gave her serial number, then said "I am a monument to all your sins." The very words that Gravemind said when the Chief and the Arbiter first met him under the library on Delta Halo.

It's very possible that she shares her creator's memories. Also, during the opening sequence of H3, Cortana is talking about how John is different, in that he has 'luck' on his side; one of the things that Dr. Halsey tested the children for is 'luck'. In the level Crow's nest, she appeared several times and repeated the patriotic words that Dr. Halsey had told the SPARTAN-IIs when they were brought to Reach as children. In the hive that was once High Charity, you can hear her say the lines that Dr. Halsey had said to John when they first met on his homeworld. "Can I speak with you please? What's your name? It's very nice to meet you. You like games, so do I." Later on in that same level, she says: "I'm just my mother's shadow..." This is a reference to Dr. Halsey.

Cortana's role in Halo 3[]

The May 2006 announce trailer for Halo 3 contains a flickering and corrupted image of Cortana's face several times while she says the words:

"I have defied gods and demons.

I am your shield, I am your sword.

I know you; your past, your future.

This is the way the world ends."

It has been speculated that the "shield" she is referring to could possibly be the Dyson Sphere (seen in Halo: Ghosts of Onyx) which can protect the humans from the deadly pulses from the Halos, as well as from the Flood infestation. It is also worth noting that, in "Ghosts of Onyx," it is discovered that Onyx is called a "shield world" by the Forerunners. The "sword" could be the Halos themselves which could destroy all life and thereby starve the Flood. The "past" may also refer to the Forerunners and their technology, which are also the "future" as they hold the only hope of defeating the Flood.

Furthermore, Cortana's line about gods and demons has lead some to believe that it is a cryptic statement spoken by the Gravemind, through her. The Covenant see the Forerunners as "gods," and the Master Chief as a "demon." In the Halo 3 ARG "Iris," more and more information is being revealed that shows the Forerunners were at war with the Flood, and only activated the rings as a last resort. Indeed, if the Gravemind, the central mind of the Flood, caused the downfall of the Forerunners, he could boast that he has "defied gods"--especially since it is shown that Gravemind has absorbed the body of the Prophet of Regret, and therefore knows everything Regret knows, including the fact that the Covenant see the Forerunners as gods and the Master Chief as a demon. The Gravemind meets the Master Chief during Halo 2 as well. The Chief is at war with the Flood, but comes face-to-face with the "leader" of the Flood, and is sent on a mission by his enemy, which he carries out without question. Later in Halo 2, Cortana tells the Chief, "That creature, the Gravemind--used us. In Amber Clad was always its intended vector." Since the Gravemind sent the Chief on a mission for its own benefit (stopping the firing of the rings, which would destroy all the Flood's food), ultimately ending up capturing In Amber Clad (it can be seen crashing into High Charity during a level in Halo 2) and sending out Flood-controlled dropships, it can also boast that it has "defied demons." If Cortana is indeed controlled by the Gravemind, nearly all of her/their statements can be traced back to information that the Gravemind would have and be able to speak about.

One storyboard listed on Bungie's website also shows Cortana seemingly screaming in pain.

In the December 2006 TV commercial, after the Master Chief pulls on his helmet, a voice sounding much like Cortana's says "Chief, leave me!". - Although some debate this as "Chief, don't leave me," or alternately, "Chief, believe me" as it is hard to hear. Or could it be "chief, forgive me!". Ultimately, however, it is most likely that the Master Chief is hearing her voice in his head saying "Chief, leave me!"--a memory or flashback from when he left her in High Charity's systems. At the end of the second to last level in Halo 2, "High Charity," when the Chief is meant to jump into a power conduit to board the Forerunner ship to Earth, Cortana urges him on, saying things like "Don't worry about the Flood, you have to get to Earth!" Finally, if the player waits for a significant amount of time, Cortana will actually say "Chief, leave me!" in the same pleading tone as seen in the December 2006 trailer. It is most likely that the Chief regrets leaving Cortana behind, especially if speculation that they have grown close to each other is true.


  • On the Halo 3 Beta in the map High Ground inside the first one of the bunkers contains a screen that observes a corridor but occasionally changes into Cortana's face for a short time.
  • In the The Legends of Charlemagne, a version of ancient European Mythology written by American author Thomas Bulfinch in the 1850's, there is a story about a Danish prince named Ogier who after pleasing the Emperor in battle was given knighthood and a sword which a fairy, named Morgana, had inscribed, "My name is Curtana, of the same steel and temper as Joyeuse and Durindana", Joyeuse being the name of Charlemagne's sword, and Durindana the name of Charlemagne's knight, Orlando's, sword.
  • Now in context with the Halo Universe. Cortana is like Master Chief's sword (In the Halo 3 Trailer she even says, "I am your shield, I am your sword.") always coming to his aid and more of an object or weapon than a person.
  • Also in the Bungie game, Marathon, there is an A.I. named Durandal which is the English name of "Durindana" which in the above legend is one of the swords which "gives birth" to Cortana. So in the same vein you could say Bungie is saying that the Durandal (A.I.) is the like the father of the Cortana (A.I.).
  • In Halo 3 Cortana frequently makes short, disturbing transmissions to Master Chief, referencing the theory of Cortana's Rampancy due to the Gravemind.
  • The first section of Cortana (Level) is called 'Rampant'
  • The accuracy of Cortana to real-life females greatly increases in each sequel to the original game.
  • She us used in the new Windows phone OS as a personal assistent.
  1. Halo: The Flood, page 26