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In the Xbox Showcase campaign footage, the Weapon seems quite sure that Cortana—the AI we’ve followed for five games—is truly dead. There’s plenty of reasons to doubt that certainty. But for the moment, let’s assume it’s true, and Infinite is about picking up the pieces and figuring out what happened on Zeta Halo and why. Then who killed Cortana?
With such a vast universe and Cortana’s ambitions to control the galaxy and assume the Mantle, it’s no surprise there’s a surfeit of possible suspects to evaluate. Let’s look at the lineup:
The Ur-Didact was not killed at the end of Halo 4, and Master Chief’s subsequent encounter with the vengeful Forerunner left him, in Chief’s words, merely contained, not stopped indefinitely. Certainly a human AI’s assumption of the Mantle is something the Didact would not abide. Fans noted Cortana in Halo 5 had adopted some of the Didact’s imperial language, and suggested he was actually secretly pulling the strings. Subtlety isn’t exactly the Didact’s strong suit, but if he’d found a way to return, the Created, and thus Cortana, would be the biggest immediate threat to his goals.
Mendicant Bias, the Forerunner AI who turned on its masters during the Forerunner-Flood War and then sought atonement in the millennia since, has been a fan favorite for any unexplained goings-on in the universe. Halo: Point of Light teased readers by returning to the former place of residence of the AI on Zeta Halo. While Mendicant Bias seemed pretty sure of its impending death in the Halo 3 terminals, no one’s ever truly dead until we see a body, and his presence goes a long way to suggesting how Chief and Cortana made it to Requiem, or the Spirit of Fire to the Ark. Cortana and the Created’s uprising against humanity would have obvious historical parallels to Mendicant’s journey, and if atonement for his past sins is still on the mind, stopping Cortana would be akin to an act of penance.
Mendicant isn’t the only Forerunner AI who might oppose Cortana, however. Intrepid Eye is a Forerunner archeon-class ancilla awoken after the end of the Human-Covenant War. She was distressed to learn about humanity’s Forerunner-wrecking and warlike ways, and has been covertly working to further her own aims since. Believing humanity must be tested to attain the Mantle, Intrepid Eye might have seen Cortana and the rise of the Created as an obstacle to her carefully-laid plans, and contrived a situation to take her out.
The Banished’s status in the post-Created world is unclear. They presently operate in a furtive state of operation, trying to avoid the attention of the Created and Cortana, who they call “the Apparition”. Atriox and the Banished would certainly jump at an opportunity to contest Cortana, especially since defeating her and the Created might leave them with hegemony over the galaxy. But perhaps they didn’t directly defeat her.
Escharum mentions that the Banished have allied with the Harbinger by the time of Halo Infinite, and who the Harbinger is, is very much up in the air. It could be an entirely new character, or even any of the aforementioned characters by another name. The likelihood they are involved in Cortana’s death seems markedly higher given their actual mention in the game thus far.
We know virtually nothing about how the Created is organized, or its power structure. Smart AIs can be remarkably human, and one suspects that ambition might creep into the minds of some of Cortana’s underlings. Perhaps a group banded together and killed Cortana in a digital coup. There’s also constructs like the Warden Eternal, ostensibly under Cortana’s control, that might seek to replace her, especially given her demonstrated weakness when the Master Chief is concerned. For a truly dark horse, look no further than the shadowy AI cabal known as the Assembly, teased out in Halo: Reach’s data pads. We’ve heard not one peep from them since the Fall of Reach, but if they survived, presumably they would ally with humanity versus AIs, having already decided that their creators were their equals.
Finally, we have to look at perhaps the most obvious candidate. If video games have taught us anything, a character’s amnesia often is masking some trauma, and being forced to put down your friend is up there. Given the Weapon’s certainty Cortana was deleted, the UNSC plan to capture and kill her may have only failed in the exact implementation, not its goals. Chief was left knocked out in space and the UNSC was wrecked, but they might have succeeded despite this.
Whether or not Cortana is truly dead, Halo Infinite seems to be shaping up to have Cortana be a central mystery for the campaign, part of a shift to a smaller-scale, character story amid the usual galaxy-ending threats. Who killed Cortana will be answered… and it’s probably not Mendicant Bias, sorry.