5. Gregor Clegane, "The Mountain"
Okay, so this dude may be one of the few characters in Westeros who may not even have a good side. Violent, cruel and abnormally large, this man has one of the worst tempers ever and basically no moral conscience. His most vicious acts include burning his brother's face, killing babies, raping, and pillaging. According to The Hound, he once killed one of his own men for snoring.