Halo Alpha
Halo Alpha

This topic appears in the TV series. For information about the game version, see Cortana.

“When the game is over, the king and pawn go back into the same box.”
— Cortana when awakening in Emergence

Cortana is an artificial intelligence who serves as an advisor to Master Chief. Designed and programmed by Dr. Catherine Halsey, Cortana develops thoughts and beliefs of her own that rival that of her creators orders. She becomes a companion and trustworthy ally to John.



While visiting Dr. Halsey's lab, Admiral Parangosky reminds Dr. Catherine Halsey that her project has not been approved, as she was meant to cease all progress on clones. Dr. Halsey lies that she did pause the programming, but Parangosky sees through her lie and orders her to shut it down. When Master Chief goes AWOL following an interaction with an unidentified artifact, Halsey once again brings up how the Cortana system could be an asset to them, but Parangosky again, shuts her down. A flash clone of Halsey, and the basis of the Cortana system, remains inactive and incomplete inside an incubator pod.[1]

Halsey undermines Admiral Parangosky by pitching the Cortana system to the council. She explains that it will overwrite Spartan consciousness and replace it with an artificial general intelligence. She believes it to be the next state in human evolution. The Spartans were the first step, while Cortana is the upgrade. Cortana represents the sum total of every available date point, holding the intelligence of the galaxy in her mind. She hopes to use Cortana to create Spartans who are more lethal, their judgement error-free, their performance upgradeable, and controllable. Captain Keyes reasons that Spartans such as John are people, but Halsey disagrees as he's much more than that. She thinks the Cortana system can help them win the war against the Covenant. Jenma points out that Halsey's previous theories depended on biological substrates derived from the illegal practice of human cloning. Halsey, however, has found a way around that. Parangosky reluctantly authorizes a trial of the Cortana system. Halsey returns to her lab where she removes the barrier around her clone, making the being open her eyes.[2]

Halsey's clone is now awake and aware that Halsey created it to obtain vital organs from herself without harming her true body. Halsey collected samples of her tissues and used them to create the clone. The clone retains emotions, thoughts, memories, and feelings that Halsey had during the time the tissues were initially taken. It has no active memories beyond her point of inception, as it did not inherit Halsey's new memories or thoughts. As it compiles the Sorvad solids before it, the clone deduces that Halsey is after its brain. Halsey explains that she has perfected the method of real-time neuroelectrical imaging, meaning the Cortana system is viable and can be integrated into a working Spartan.

Adun and Halsey work together to activate a scanner that digitizes the clones facial features, then holds open the eyelids while a needle pierces the eyeball. When the neural substrate acquisition is complete, the clone has died, and they use another machine to implant the needed mechanisms and information into John's mind. Adun destroys the clone in a tub of acid that effectively disintegrates the body. While John remains in stasis, Halsey calls Cortana who appears before Dr. Halsey. As they are acquainted with one another, Halsey explains that she's going to run some tests on the artifact John found on Madrigal to determine its provenance and functionality. Cortana changes the subject - her neural implant is working perfectly, but she can't take full operational control of the subject. Halsey has limited her access to the reticular formation, which upsets Cortana, as that goes against her directive. Halsey recommends she use John's downtime to familiarize herself with the trove of human knowledge available to her. Cortana reveals that it will only take her 7.6 minutes out of the hour given. Halsey assures Cortana that she'll be kept very busy.[3]

Partnership with Master Chief[]

Halo S1 First-Look Cortana

When John awakens, he has little interest in meeting Cortana or interacting with her. He does, however, comment on her resemblance to Halsey. Cortana states that it's nice of him to say, as her features were made to feel familiar with her voice and accent designed to be pleasant. She contains a hollow particle elixir that allows her to appear in an environment. Cortana views this as a partnership, while John wants to command her. She is coolly dismissed by Halsey. John doesn't approve of the new partner but Halsey is certain it is a great leap forward for everyone. When John begins his tests with the object, Cortana places John in stasis to access the object, which ends the connection between John and the artifact. When Cortana releases John it activates the object again. Cortana is upset that she's being used as an assistant, but Halsey reminds her that she was created to follow her orders. John returns to Spartan Headquarters when Cortana appears to introduce herself to the team. John snaps that he didn't summon her and tries to dismiss her, but she only questions his vernacular before politely excusing herself. John remarks that the new A.I. is not permanent.

John attempts to search for the place in his visions, and Cortana offers her help, much to his annoyance. He relents and she finds 103 potential matches, and he's been to 23 of the planets through Spartan deployments. He recognizes Mamore as the place where they lost Nora 098. He remembers losing her but doesn't feel anything over the loss. The hormone pellet in his spine suppresses adverse emotional responses and protects his mission readiness. When he touches the artifact he doesn't just see the memories - he feels them. Cortana contacts Halsey to warn her that John is removing the emotion regulator. Halsey wants Cortana to help him so he'll see her as an ally and not a spy. Cortana reluctantly agrees and helps John remove the pellet. He even thanks her for the help and she reminds him that she's here for him.

She later helps him explore Reach without his pellet, listening to him as he admits that he came to not only hear the music differently, but hear the music the way everyone else does. He returns to the testing bay and demands Cortana open the door, which Halsey allows her to do. Cortana warns him not to touch the artifact as it stresses his heart and nervous system. He ignores her as he grabs the artifact, triggering a vivid memory. When it ends, he asks Cortana how many planets on her list have visible ice rings from the surface. She shows him the place from the barracks, and it's Eridanus Two - a planet that wasn't always uninhabited. From Cortana's holograms, John learns about the Reach for Life project and a plague that desolated the inhabitants of the planet. He was evacuated and adopted at age six. He wants to know about his parents, with Cortana admitting that the remaining population were sealed off on the planet to contain the virus. She is surprised by the emotions he feels over his parents, but they are interrupted by Halsey. As Adun and Halsey discuss the dangers of John's memories, Halsey admits that if John remembers too much, that Cortana was created for just that reason.[3]

She guides Master Chief when the arrive on Eridanus II, happily reconstructing his childhood home for him using fragments of what remains. She is amazed and curious when he continues to experience vivid, lucid memories despite her removing the projection of his home and the absence of the object.[4] She proves herself to be a sassy helper despite the dismissiveness John has of herself. She likes Kai's hair even if it is an act of rebellion. Cortana advises John not to interact with the larger keystone again, but he ignores her warnings of not being healed since the last interaction, and activates it once more. These visions show him that he was kidnapped as a child by Halsey, who he angrily attacks. Cortana puts him into stasis mid-jump and he collapses to the ground. When he awakens, he is surprised to learn of her capabilities to shut him down. He demands Halsey's location but Cortana refuses to give it. Slipspace is breached by the Covenant and a viscous fight ensues, though Cortana's helpfulness on the field is indisputable. John disobeys orders to deliver the artifact to Dr. Keyes' ship and instead, saves Kai and the marines. The artifact is ultimately stolen by the Covenant, though they leave behind what Cortana identifies as a human woman.[5]

Halo 106 Cortana-John

Once the battle concludes, Cortana urges John to seek medical attention as the connection with the larger artifact caused quite the strain on his physical status. He tells her to shut up and tries to ignore her foreboding warnings and disagreements over his health. With the ship empty except for himself and Halsey, John seals her inside the UV decontamination room. Cortana tries to understand why he's acting out, initially believing it to be a result of the artifact. John clarifies that he's never felt better. He activates the decompression chamber which will release a high dose of radiation that will burn and liquidate Halsey. Cortana pleads with John to release her while Halsey screams out for him, the clock ticking down. John demands that Cortana take control of his body and force him to open the door, otherwise her creator dies. Cortana doesn't have that ability as she can only overload his neuro pathways to place him in a temporary stasis. He doesn't believe her. The clock runs down and the radiation begins, so John saves Halsey before slamming the door shut. He needed to test the limits of Halsey's AI system but doesn't play to save her from what's next. As he storms off, Cortana apologizes to Halsey before evaporating.

As the day progresses, John learns more about Halsey's role in his abduction and the Spartan program's beginnings. Cortana continues to press John to seek medical attention but he angrily lashes out at her to leave him alone. She's trying to help and can help him find what he's looking for, but he doesn't believe she can. She tries to discourage him from touching the smaller artifact, which they refer to as the Halo, but John is stubborn. She asks what she's supposed to do now and he tells her to fix a problem - the galaxy is full of them.

Meanwhile, Halsey is removed from her lab and stripped of her access to the UNSC database, but has Adun steal some technology before their mutual excommunication. Halsey believes that Cortana will find a way through Adun's algorithms and firewalls as she isn't designed to give up. Cortana succeeds in reuniting with Halsey, feeding her information on John's activity, including his impending connection to the smaller artifact. She shows Halsey both John and Makee's vitals during the connection and they learn how the pair are inexplicably linked during contact.[6]

Despite Halsey's exile from the Spartan program, she stays apprised to everything happening thanks to Cortana, who serves as her spy. The AI finds herself in a complicated situation when John and Makee have sex, as she relays the closeness to Halsey, citing his rise in dopamine levels. She believes John's realized he's special and not alone in the universe anymore. Halsey snips back that he's always had her, so Cortana reluctantly agrees that she's right. She then relays that Makee is set to interact with the artifact around noon, which pleases Halsey. She has a plan to intercept the artifact, Makee, and John, though she isn't specific over whether to capture him alive or dead.

Battle for the Halo[]

Halo 108 Cortana

Halsey uses a contact lens that duplicated Miranda's retinal ID to gain access to her lab again and other UNSC systems. She broadcasts herself to Makee in an attempt to sway her to Halsey's side, which Cortana visibly disagrees with. When Makee turns her down, Halsey invokes "Zed Protocol". She tells the Spartan members of Silver Team that the UNSC cannot be trusted. Kai questions the orders so Halsey instructs the other Spartans to eliminate her so they tie her up. Cortana becomes increasingly uncomfortable with the situation as Master Chief is walking into a trap set by Riz and Vannak.

Her discomfort increases when Halsey reveals that she doesn't need John as Makee can activate the artifacts. Cortana can finally fulfill his creation place to place John in stasis and completely take over his body. She belives that Cortana, operating through Master Chief, will be the very best of everyone. Cortana, disagreeing with the ethics of the plan, betrays Halsey to warn John of the trap. She cuts the ships connection to the FLEETCOM base. She then helps John fight against Vannak and Riz, though he's underequipped for the fight and badly beaten. Kai arrives and helps John until they reach a stalemate. Before they can continue the battle, Makee makes contact with the artifact and sends an energy blast across FLEETCOM.[7]

The Spartans split up with Kai heading to stop a fleeing Halsey while Riz, Vannak, and John try to stop Makee from leaving with the artifacts. Both teams fail, leaving John, Cortana, Parangosky, and Miranda to find the Covenant planet High Charity. John works flawlessly with Cortana to decode the Covenant prophecy, ultimately realizing where the planet might be located.

Silver Team boards a space craft and heads into space. Cortana also tells John of Halsey's plans for Cortana to take over John's body forever. She concedes to waiting for the less beat up version. Later, Cortana warns the gravitational pull of a meteor area will be tricky to navigate as one wrong move with "spaghettify" the ship. John gives blind trust to Cortana as she calls out directions to John who keeps his eyes closed. They arrive with a stealth plan to a nearly vacant area. As they advance their cover is eventually blown, triggering thousands of Covenant forces to emerge from the grounds to attack them.

Halo 109 Cortana

An intense battle ensues as Silver Team is quickly overwhelmed. John is taken out by Makee who makes contact with the keystones. He awakens when Makee dies, with Cortana warning that they don't have many options left. They can either save the Spartans or get the keystones, but John can't do both without losing both. Silver Team is badly injured and can't fight much longer.

He surrenders his body to Cortana as she can save both the team and the keystone. She is reluctant she isn't sure she can pull him back or repair his psyche once she assumes control. He relents that he trusts her and gives himself over to the Covenant to attack, which forces Cortana's hand, as his body is dying. She projects out of him to put her hand over his now still heart. She then assumes control over him and quickly demolishes the Covenant forces. Master Chief carries out the artifact and leads the Spartans aboard their ship where they take-off into the sky, having won this battle. Riz is severely injured so Master Chief silently cauterizes her wound before assuming control over the ship as the pilot. Kai joins him and reluctantly asks John if he's in there. Master Chief silently stares out into space.[8]

Advising Ackerson[]


The UNSC doctors sever the tie between Cortana and Master Chief, ripping them apart despite the medical uncertainty of such an event.[9] Six months later, Cortana serves as an advisor for Ackerson, who took over for Dr. Halsey as head of the Spartan Program. Ackerson asks Cortana for a projection and she responds that there is a 97% likelihood "it" will happen no matter how she runs the simulations. He promises to try and come back to see her, but she knows that's not true. He won't be able to return because of the simulations.[10]

Covenant Abduction[]

During the Fall of Reach, Halsey leads Soren to where Ackerson is keeping Cortana. They briefly reunite before Elite attack, having infiltrated FLEETCOM. Makee grabs Cortana's device and disappears with her.[11]


Cortana is an AI whose personality is a combination of artificial and natural. Having been created from a flash clone of Catherine Halsey's brain, Cortana has some of her personality traits and worries. Cortana 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. She is helpful and eager to be of assistance to Master Chief, taking his dismissal of her existence. She slowly learns to emote and develops a witty and playful personality with a small sense of cryptic humor laced with sarcasm. She begins to empathize with John as she senses his emotions and makes emotional pleas to him.

Behind the scenes[]

Cortana is based on the Halo video game character, Cortana. They are both voiced by Jennifer Taylor.