#2 Illidan
You may not be prepared to truly try to understand Illidan, but there’s a reason for which he got to become the bad-ass that he is. See, he was one of two brothers, and they were both quite awesome, but his brother got the girl he loved. He took it alright, considering, but he liked power, and as we know from some childhood stories, power corrupts. Even more so in the world of Warcraft. So he became the reason the Sundering happened. And then was imprisoned for 10 000 years after trying to fix it. His brother’s girlfriend breaks him out and he helps, but then makes another blunder that he tries to fix by absorbing demonic power.
He’s the prototypical example of the saying that “The road to hell is paved with good intentions” but in his case, it was the Burning Hells that got him in the end (aside of the raid that downed him on top of the Black Temple).