Kain (Dissidia 012)

"I was brainwashed! No, I mean this time I REALLY was! By a Moon alien!"

"I was controlled by Golbez but I actually enjoy it since I can get a laid who's my best friend's girlfriend but please forget everything and let me join your party again."

Part-time Dragoon of Baron and Full-time backstabber, Kain first appeared in Final Fantasy IV.

He was friends with Cecil since childhood and always had a thing for Cecil's girl Rosa Farrel. As they grew up Kain's swag was stolen by his friend and so he grew to be a jealous hater. In order to not seem as pathetic Kain developed an ingenious plan; he pretended to be brainwashed so he could steal the Crystals, steal his best friend's hot white mage girlfriend and just wreaked havoc. He changed his mind after and turned good, but changed his mind again and did this for about 40 times within the first game.

His friends were dumbasses so I can't really blame him if they kept falling for the same old tricks.