The following contains spoilers for Halo 4, if you have not completed the campaign we recommend you do so before reading on.

Cortana has always been one of the most fascinating parts of the Halo fiction for me. A.I.s in the Halo universe are just very interesting in general; they’re based on the neural pathways of a human brain, which means their initial intelligence is that of a human, but they can perform far more simultaneous tasks and acquire more knowledge than any one human ever could. This comes at a price, however, with one of the core conceits of their existence being that they only have a lifespan of around seven years. These so-called “smart A.I.” (there are “dumb” A.I., too, who don’t deteriorate) acquire so much information that eventually they just cannot process it all and quite literally will think themselves to death. This is known as Rampancy, and often sees the A.I. turn against their masters as they begin to fully comprehend the finite nature of their existence.

This brings us back to Cortana, who at the start of Halo 4 has been in operation for eight years. Four of these have been spent in almost complete isolation, floating through space. Cortana isn’t like most A.I.s, either. For starters, she’s based on the brain of a young Dr. Catherine Halsey, the creator of the Spartan program. Secondly, Cortana has experienced a lot more in her short time than most. She spent an extended period of time inside a Halo’s master control room, during which time she had access to more knowledge than she knew what to do with. Shortly after that she was the captive of the flood hivemind known as Gravemind, a time which we know very little about. Though we did get hints of Cortana’s struggle in Halo 3, the messages she sends to Chief show her in great distress.

Once Chief recovers her, however, she seems like the same old Cortana. But fast forward to Halo 4 and we immediately see a very different A.I., and I’m not talking about her shiny new character model. Cortana is now far more emotive than she was before – even her voice has a completely different tone. Before she was pretty much all business, with the occasional wisecrack slipping in for good measure. In Halo 4, her voice is continually strained, and we see anguish on her face more often than not. Her brief existence is coming to an end. She knows this, and it scares her.

343 Industries has done a masterful job of bringing humanity to a character who isn’t even human. Thanks to the fantastic voice acting of Jen Taylor and performance capture of Mackenzie Mason, you’d have to have a heart of steel to not feel for Cortana. Throughout the game we see her lose control of herself, as her “mind” tries to keep itself together. Fragments of old memories burst to the forefront, and we see near-literal explosions of anger come from seemingly nowhere. The parallels with mental illness are easy to see, and it’s hard to watch it happen to a character we’ve know for 10 years.

It’s not so much that 343 has made me care about a character in a video game, because that’s certainly happened plenty of times before. It’s more the fact that they managed to evoke those feelings for a character who is removed from and arguably of humanity. She’s a naked blue lady for crying out loud; if anything, she should make me feel uncomfortable. Instead, what she looks like doesn’t even enter my mind. All I see is a person dealing with her mortality, and it breaks my heart. The portrayal from writing to acting is just so well executed that it’s nigh impossible to not become engrossed.

Through Cortana’s torment, we also get to see more of Master Chief, who up until now was just the stoic action hero who rarely said anything of note. But now he’s stuck in denial, clinging to the false hope that if they can just get to Dr. Halsey, everything will be fine. She tells him that it won’t work, that she can’t be fixed, but he doesn’t listen. He just reiterates that they need to find Halsey. Even when she puts the mission, and his life, in danger, he still won’t admit the inevitable.

Cortana has been the one constant in his life, with anyone else he could consider a friend either dead or presumed to be so. He often struggles to mask the sound of fear in his voice, and when Cortana finally says goodbye, his body language turns him from a hulking armored soldier to that of a small child feeling helpless and lost. While the main story may have fallen short, 343 nailed the relationship between Cortana and Chief.

It leaves us with a Master Chief who is now lost, that guiding voice in his head is gone. Halo 5 should be very interesting, as we see Chief deal with his loss, and one has to wonder who will replace Cortana. Will it be an entirely new A.I., or will they go with the familiar in another version of Cortana? Though as our Cortana said, “it won’t be me.”