Jesse Rayner

What if there's a plot for Cortana to come back in Halo 5 or 6 as the antagonist? Here's my line of thought: In Halo 2 at the end of the level High Charity we see Cortana and Chief split up, and towards the end of the game we see Cortana with Gravemind. In the level Floodgate, when Chief recovers the oracle with Cortana's message, it seems as thought there's degradation in her phsyche or personality. This is shown once again in the level Cortana when Chief finds her, and further more when she starts to babble and utter nonsense when they're on their way to the Pelican. If we stick to the story line put place in Halo 4 those are the first moments when we see the very beginnings of her rampancy. As the story progresses in Halo 4 we see her slowly starting to fall apart until finally she completely loses it in Composer. Finally, in the last level, she appears in a physical form, meets with Chief, and leaves. This is my theory: Between the time when Cortana is separated from Chief in Halo 2, spends time with Gravemind, and is recovered in Halo 3 she has, in essence, become institutionalized by Gravemind, resulting in her turning against the human race. She is able to use her knowledge of the human race from the time since she was created up until now to devise a way to get rid of them. This theory can be supported by another instance where Gravemind institutionalized another AI, turning it against it's creators. 05-032 Mendicant Bias was the most advance AI of his time, created by The Forerunners, tasked to defend against the Flood. This AI is brought up in transcripts in the terminals in Halo 3 which tell of this story. This goes back to Cortana. At the end of Halo 4 she defends Chief during his encounter with the Didact, I think she could have done this to help lead Chief into thinking she is still on his side, which also eliminates an opponent of Gravemind's. Now she is also able to gain physical form using Forerunner technology, which is shown when she physically meets with Chief before leaving him. Something else I've though about is what if Cortana's rampancy is showing her true side, showing a much darker side, and the rampancy was actually causing he to lose control over hiding it? This could have also forced her into taking a physical form, eliminate the Didact, and separate herself from Chief. As a player of the games since Halo CE, reader of the books, and an avid follower of the Halo Universe, I have been extremely pleased with how the story of Halo and the universe has formed. IF there was any truth behind this theory I would be extremely mind blown and rather impressed by how Bungie/343i formatted the games to lead up to this. Of course this is all just theory.