1. Cortana
"Thanks for the tank. He never gets me anything." Throughout this article, I've made an assumption that you've played Halo 4. If you haven't, probably should've stopped reading earlier. But, spoiler alert, there's some emotional information lurking just beyond this paragraph that'll make you weep like a grunt. When you're being chased by body-eating zombies, there's nothing more comforting than a sarcastic hologram to keep your spirits up. To me, Cortana truly is a character and concept like no other. Cortana has a special place in my heart reserved only for the greatest things in life like lasagne, Pearl Jam and... now virtual blue women, apparently. Her witty comments make her not only the most intelligent character in the series, but certainly the most amusing. Her development from just a little helper into your only friend is the work of literature genius. Whether Cortana will return is yet to be seen. But given the affinity that most Halo fans share with her, I wouldn't be too worried.