Lord Yggdrasil from Tales of Symphonia.
He split a planet into two separate worlds and created a system that lasted for 4000 years that involved the manipulation of the populace to worship a false goddess, the sacrifice of chosen people to revive his sister that was killed, had no problem with sticking humans into concentration camps called "human ranches" to create gems that would give his followers strength, and lost his mind when his sister rejected his plans.
Above all, he's a fallen hero. He saved the world, was a good guy, but lost his faith in life when those he risked all to save killed his sister.