Just curious to know who, in your opinion, is the greatest video game villian ever. (I realize because of where these forums are, this is going to be bias, but still...)

You can consider any factor you want, not just the acts they did- think about things like:

Personality
Appearance
Motives
History behind them
Things they say
Anything else you think is relevant.

My pick: Jon Irenicus from Baldur's Gate II.
(SPOILER)He steals your soul to replace his own, which was stripped from him after a failed attempt to become a god at the expense of the elven people. In addition, there is a certain "MacBeth" dynamic, in that his sister influenced his initial betrayal, but he continued to carry through with it.

His voice acting and lines are great as well. He manages to pull of the oxymoron of emotionless hatred and depravity better than any other voice I've heard, including other genres. His attempts to get your character to embrace his heritage have such an "evil logic" quality to them that he gets my vote for the greatest villian.