A character for a story I've got cooking up, but occasionally I adapt him as a tabletop character for those rare "non-good" campaigns. Sort of a devilish type that I see as much more of a manipulator than a fighter, though instead of manipulating with sweet words and charm, he does so through sheer logic and debate until his opponent comes to believe his word is truth.
While he's definitely morally dark, I could see him becoming a little bit better as a story would go on. Likely with him coming to the logical conclusion that life is more enjoyable when you're not a complete jerk.