Dhaos, from Tales of Phantasia. Rather complex anti-villain; it’s hard to disagree with his goals, and his means start rather peaceful. He only takes the mantle of the Demon King once labelled as such… and, sure, he becomes ruthless and cruel, but you’d get like this too if you’re trapped for years in an alien planet, after your wife died so you could achieve a goal, and the goal is now unachievable.