Elizabeth is surely the best AI companion in video games, never getting in the way and yet always there with a wry line and able to open tears in the fabric of reality, and conjure ammo and turrets from thin air. Bold and direct, she’s at the center of the whole game, despite the fact that the story makes her something of an accessory over which all the men fight. Episode two of the game's Burial at Sea DLC is a tonic, then, allowing her to come into her own as a stealthy ninja manipulating the history of Rapture to enable the events of the original Bioshock to take place.
Iconic moment: When you realize exactly why Elizabeth is missing a piece of her pinky. Spoiler alert: it's the reason why all of Bioshock's temporal madness is happening to begin with.