Dango said:
I believe this has not been mentioned yet.
Whichever Sith lord that Revan and Malak found on the outer reaches of the galaxy, who caused then to turn to the dark side, seek out the Star Forge, and almost destroy the galaxy, all while just sitting back and watching, if I knew who it was, I'd give him the most awesome medal ever.
Woo! Time to geek the fuck out!
There was no Sith lord that corrupted Revan and Malak, Malak was corrupted by the (I'm not even gonna spoiler this because if you haven;t played KoTOR by now you can go kill yourself) Star Forge which was in turn created by the Rakatans, the sadistic alien race that conquered a ridiculously large portion of the galaxy.
And really, Revan wasn't corrupted by the Star Forge, because he wasn't dumb enough to rely on it's power fully, Malak was, which why you end up killing his jawless ass.
I really wouldn't call Revan any particular alignment, now that I think about it. He used both sides of the force, in what was probably the biggest Xanatos Gambit in the history of the Expanded Universe. He did what needed to be done in order to preserve the galaxy.
Obviously, my vote goes to Revan.