Ghetsis? I could say he's pretty much an evil person. I mean, in the first two games, he tried to manipulate everyone to release everyone's Pokémon so he could dominate the whole region, and in the next two games, he tries to freeze Unova (mainly Opelucid City and the other routes next to it) to create destruction to the region itself and rule it over. I say that he was a brain washer at first, then he became a mad man. That pretty much defines him very well.
And really, he tried to kill the protagonist in B2/W2; I think that was the first time an antagonist tried to kill a protagonist directly in a Pokémon game. Doesn't that make him a really evil person?