Cortana/Silver

Cortana is an artificial intelligence in the United Nations Space Command.

Creation
Dr. Catherine Halsey had plans for the creation of Cortana as early as the beginnings of the Spartan program. To this end, Halsey created a flash clone of herself that she kept in stasis for years in order to harvest her own brain to create Cortana. At the time, Halsey was unsure if human flash cloning would ever be legalized and if she'd actually be able to go through with it while sitting across from a living, breathing copy of herself.

In 2552, Halsey attempted to get Vice Admiral Margaret Parangosky's permission to create Cortana without any success. While visiting Halsey's lab following the Attack on Madrigal, Parangosky spotted the flash clone and berated Halsey for her actions. Parangosky ordered Halsey to destroy the clone and any others that she might have made. Later, as John-117 started to go rogue, Halsey again tried to get the Admiral to approve "the Cortana system" without any success.

During a meeting with UNSC HIGHCOM, Halsey suggested Cortana as a solution to controlling John. Halsey explained that, similar to how Spartan bodies had been enhanced to the limits of their current technology, Cortana would do something similar for their minds. Cortana would overwrite the Spartan minds and replace them with an artificial general intelligence. Halsey called Cortana the next stage in human evolution with the Spartans being the first step and Cortana being the upgrade. Halsey stated that Cortana represented "the sum total of every available data point. The intelligence of the galaxy in essence." With Cortana, the UNSC could create Spartans who were more lethal, had error-free judgment, upgradable performance and who were most importantly controllable. Halsey pointed out that the Spartan were the UNSC's only effective weapon against the Covenant and insisted that with Cortana's help, they could win this war. Although one of the officers expressed concern about the need for illegal flash cloning of humans, Lord Hood asked if Parangosky, as the head of ONI, was onboard with this plan. Blindsided by Halsey's revelation of her plan to HIGHCOM, Parangosky reluctantly agreed that the case of John provided an opportunity for a limited trial of the system. Hood then agreed to implementation of the program, leaving it to Parangosky to handle the technical hurdles.

Shortly after John's return, Halsey awakened her clone from stasis and filled her in on the Spartan program and that Halsey had perfected the process for neuroelectrical imaging. Halsey presented Cortana as an upgrade to a reluctant John who eventually agreed after Halsey told him that Cortana was the only way to get him back into the field and to advance their research into the Forerunner keystone.

Halsey and Adun Saly extracted the clone's neural substrate, killing her in the process. Halsey used the substrate to create Cortana while also giving John a neural implant that would allow Cortana access to him.

Moments after the procedure was complete, Halsey called out to Cortana who manifested her avatar for the first time, stating that "when the game is over, the king and the pawn go back into the same box." Halsey happily greeted the new AI who accessed John's military record and complimented his strength, stamina and instincts, calling him a natural leader. Cortana was pleased by Halsey's choice of John, but Halsey asked Cortana to access the files on the artifact found on the planet Madrigal, explaining that she was planning some experiments on it that she wanted the AI's help with.

However, Cortana warned Halsey that there was a problem: while her neural implant was operating perfectly, she was unable to take full operation control of John. Halsey admitted that for the moment, she had limited Cortana's access to the reticular formation and instead had her operating as more of an on/off switch despite Cortana's directive to integrate fully with John in order to optimize both his physical and mental performance. Halsey reassured Cortana that she would do that in time and much more, but John was a central part of the examination of the artifact and she needed to first understand how the artifact affected him and how it might adversely affect Cortana. Halsey suggested that Cortana use the hour until John awakened to familiarize herself with the trove of human knowledge that was now available to her and promised to keep Cortana very busy.

Meeting John-117
After John awakened, Halsey explained to him that the neural implant would make Cortana always available to him and he reluctantly agreed to meet her. Cortana introduced herself to John who noted that Cortana looked like Halsey herself and cut off Cortana's explanation of her role. Halsey explained that, due the system having a hollow particle exciter, Cortana could appear to him in any environment and John questioned if he commanded Cortana and where she went when he wasn't deployed, repeatedly referring to Cortana as "it." Cortana called their relationship more of a partnership and realized that John must not know what she was capable of. Halsey cut off Cortana's explanation of her abilities and Cortana awkwardly departed. John remained uncomfortable with the idea despite Halsey's reassurances that Cortana would enhance his abilities a hundred fold.

Halsey later ran a test on the keystone with John and had Cortana put him into stasis once it was activated so that Cortana could access the artifact herself. However, once John was shut down, the artifact immediately deactivated itself, leaving Cortana unable to get any readings at all. Once she released John, Cortana argued that if she was given full control of John now, her readings would be more accurate, but Halsey refused as the artifact would only respond to John as John for some reason and she was unwilling to risk their ability to interact with it.

During John's reunion with Silver Team, Cortana manifested to introduce herself to the team and to inform them that she would be working with John to provide logistical and tactical support to the team. John was furious as he hadn't summoned her, confusing Cortana and John ordered Cortana to leave, much to her obvious disappointment. After Cortana was gone, John told the other Spartans that she was a new AI created by Halsey and called the situation temporary.

Later, as John attempted to run a search on the FLEETCOM Central Database without success, Cortana contacted him and offered him her help. John reluctantly explained that the artifact seemed to be triggering memories within him and described what he was seeing. Cortana informed John that 103 colonies and moons matched the flora and fauna that he was describing and displayed the worlds for him. John recognized some of them with Cortana confirming that the Spartans had gone on deployments to 23 of those worlds. Stopping on Mamore, John recalled losing Nora-098 there, but he felt nothing at the memory. Cortana explained that the hormonal pellet suppressed adverse emotional responses and protected mission readiness and that it was a part of what made him a Spartan. While John was aware, when he touched the artifact, he not only saw the memories, but he felt them as well.

Shortly thereafter, John began attempting to remove his emotional regulator due to his visions and Cortana warned Halsey as it was against Section Three, Regulations on Spartan Behavior. Although Cortana offered to put John into stasis again, Halsey instead ordered her to help John, stating that she would take care of the regulator while John needed to see Cortana as an accomplice, not a spy. Cortana directed John on where and how to cut into his lower back and John successfully removed the regulator. Unseen by either John or Cortana, Kai-125 secretly witnessed John's actions. Cortana guided John as he traveled through a nearby city, experiencing everything for the first time in a long time without his emotions suppressed.

After seeing a dog in the park, John was struck by an epiphany and he returned to the artifact, demanding that Cortana open the door for him when it refused to respond to him. With Halsey's consent, Cortana overrode the lock for John, although she warned him against using the keystone again due to the stress that it placed upon John's heart and nervous system. Afterwards, John revealed to Cortana that there was a second artifact which he'd drawn over and over and that he must've seen it as a child. John now remembered that the planet he had lived on had ice rings visible from the surface and Cortana determined that there were only three planets matching that description from their earlier search. Cortana showed John the three planets and he identified the correct one as Eridanus II. Cortana filled John in on the history of Eridanus II from the information available to her, including that most of the population had died off due to an incurable plague and that the planet was sealed off as a result. However, Cortana was unable to find any specific information on the fates of John's parents for him.

Cortana was able to generate a holographic image of the Eridanus II keystone based on John's description of it. Although Adun worried about what other memories the visit to John's home planet could unlock and the impact that it could have, Halsey reassured him that that was what Cortana was for. On the bridge of the ship to Eridanus II, Cortana watched John before walking away with a worried look on her face, apparently genuinly concerned for John.

Production notes
Cortana in Halo: The Television Series is portrayed by Jen Taylor. Natascha McElhone was originally cast to play both Cortana and Catherine Halsey, much like Jen Taylor did for Halo 4, Halo 5: Guardians, and Halo Infinite. However, due to scheduling difficulties caused by the COVID-19 pandemic, McElhone was unable to complete her work as Cortana, so Jen Taylor was brought onboard the project to reprise her role from the games.

List of appearances

 * Halo: The Television Series
 * Contact
 * Unbound
 * Emergence
 * Homecoming