Cortana

"Don't make a girl a promise...if you know you can't keep it."

- Cortana

Cortana, UNSC AI number 0452-9, (voiced by actress Jen Taylor) is a character in Halo: Combat Evolved and Halo 2. Cortana is a smart A.I., meaning she has the ability to learn and adapt, but also making her capable of going rampant. 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. 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.

Cortana was designed to infiltrate computer systems, and she is very good at that task. 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. A side effect of her origins are that she is said to resemble a younger Doctor Hasley physically 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 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 current loyalty is somewhat in question, however.

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 inhuman 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.

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. 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 knowlege of the Foreunners and the Index.

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 in a ship on High Charity in a position to detonate the ship and destroy the the covenant city. 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.

Finally, the 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 agressive 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."

Rampancy in Halo 3
In the Halo 3 Announcement Trailer, Cortana says: "This is the way the world ends." Perhaps she is falling into some form of melancholia, and believes that there is no hope of shutting the rings down for good, or that ending the threat of the rings and/or the Flood will require Earth to be sacrificed. Another possibility exists that she has in some way been compromised or placed fully under the control of the Gravemind. This theory can be likely since in the Halo Graphic Novel and in Halo: The Flood it is shown that the Flood absorb the knowledge of their host like with Keyes in order to acomplish a goal. Thus as long as a Flood infected a host with knowledge of 'smart AIs' it is possible that she is entirely under Flood control, or alternatively, it could be the other way around, where Cortana has absorbed all of the Gravemind's knowledge and has become transcendant.

To further affirm this theory, Frankie wrote on Bungie.net: "Her reprised role in Halo 3 will probably be a challenging one, since Cortana’s circumstances are considerably darker and more terrifying than in prior appearances. One thing you already know from Halo 2 – she’s not with the Chief now, but rather, in the clutches of the Gravemind on the ruinous High Charity."

Cortana's role in Halo 3
The May 2006 announce trailer for Halo 3 contains a flickering 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 which can protect the humans from the deadly pulses from the halos, as well as from the flood infestation, while the "sword" could be the halos themselves which could destroy the covenant 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.

Whether Cortana is experiencing rampancy is up for debate.

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".

Trivia

 * 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 Cortana, 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.).