Villainous Big Bang

If you have seen Avatar: The Last Airbender, then you would know Jet. He plays a rather important role in the avatar's journey, helping him take down the corrupt Dai-Li in Ba Sing Se, and many would say that makes him a hero. But that would be heavily erasing villainous deeds of the past. Jet was passionate, no doubt, and he certainly had a sympathetic story and reason, at least for him. But when it came down to it, he was willing to use anyone and anything to reach his goal, no matter their innocence. The main characters trusted him, mostly, but he used that to trick them into helping him wipe out an entire village of innocent people in order to get to a few fire nation soldiers. The story, and the characters, definitely don't excuse his behavior, even with the backstory (in fact many of the Good Guys who give a hoot about saving innocents have the same theme of backstory).