O'Brien from 1984/the Party of Ingsoc. It cant get any worse than this. Even a villain trying to kill everyone is not as terrible.
"The old civilizations claimed that they were founded on love or justice. Ours is founded upon hatred. In our world there will be no emotions except fear, rage, triumph, and self-abasement. Everything else we shall destroy...everything."
"We shall abolish the orgasm. Our neurologists are at work upon it now. There will be no loyalty, except loyalty towards the Party. There will be no love, except the love of Big Brother. There will be no laughter, except the laugh of triumph over a defeated enemy. There will be no art, no literature, no science."
"There will be no curiosity, no enjoyment of the process of life. All competing pleasures will be destroyed. But always- do not forget this, Winston? always there will be the intoxication of power, constantly increasing and constantly growing subtler. Always, at every moment, there will be the thrill of victory, the sensation of trampling on an enemy who is helpless."
"If you want a picture of the future, imagine a boot stamping on a human face- forever."
Others( of course not that awesome)
Most of the races in the Warhammer 40k-Universe(even the friendliest races like the tau or eldar would be considered villains in any other fictional universe, building concentration camps or killing millions of humans to save one of their kind)
Fontaine/Atlas from Bioshock...ah you know what:make it the whole lot, Ryan, Fontaine, Tennebaum, all manipulating me:/...uh! I forgot someone! Sander Cohen, the artist(is that his name?) While the world around him goes to pieces he's still searching for aesthetic perfection...creepy guy.
Uh yes and the combine. Exploiting the whole planet, assimilating species into their army after harvesting their bodies for useful stuff and filling the holes with cybernetic implants(why needing a full brain when you can have half a brain, lotta microchips(making you a remote-controlled tool) and a funky mask?
From that perspective I've always felt miserable killing striders and gunboats(its like killing an elefant with microchips in his brain and a lasergun mounted on his head...it can't do anything against it, its just a running carcas...thinking about it I think I shouldnt.