Potato GLaDOS from Portal 2
It’s rare to see any character transformed from a villain to an ally, but in Portal 2, players were treated to just that. While the AI GLaDOS had been the embodiment of an enemy in the first game, the sequel saw her give up the sense of superiority in exchange for humility — being uploaded into a potato battery will do that to you. The lessons GLaDOS learned while confined to the potato and forced to cooperate with the player against a common enemy may not have lasted, but it was a heck of a trip while it did last. Plenty of sidekicks crack jokes at their hero’s expense, but none so well, or so cruelly, as GLaDOS.