Illidan Stormrage from warcraft 3 to the burning crusade expansion.
if you consider these spoilers then you have been under a rock quite frankly.
He is released after a fair long time, and the first thing he does is try to help the alliance, then malfurion says that he doesn't agree with his methods and straight up banishes him. No warning, no reminders that that kind of shit isn't how night elves do things, straight out on his ear. Then Illidan goes off on his lonesome, does some bad things natch, mostly out of bitterness, madness and anger. After finding a home in outland and ousting the burning legion, albeit serving a bit of a morally dodgy master, Illidan tries to kill Arthas. The main bad guy who caused a ton of suffering to literally thousands. Then in World of Warcraft canon storyline 25 so called brave heroes invade illidans home, kill everyone they see who serve him and then kill him for not doing things in a certain way.
Happy heroism everyone.