Add Simon Bar Sinister to the Old Guard Evil Geniuses ( Underdog)
And what, Tamerlane wasn't good enough to qualify? If you go to Kazakhstan, I think you can still find his palace, maybe it's in Russia proper. While we are in Russia, add Lenin, Stalin was more evil, but less of a genius. Add Rasputin. For a monk he sure worked at evil.
Roman emperors, Caligula, Nero.
I'd say the saint who coined the term, and I paraphrase here " Kill 'em all, let God sort 'em out." qualifies. But I am not a trained theologian.
Chairman Mao, and his Gang of Four.
And what do you mean to put Cthulu in the list? Cthulu is beyond morality. It has so little in common with what we consider reality, that good and evil just are not appropriate. Being made insane by being in the mere presence of a Cthuloid, well, doesn't sound like what I consider to be evil. It isn't good news, but it is not necessarily evil per se.