Who is your favorite villain in Trek?

I'm pretty stoked about the casting of Paul Giamatti as the main villain in the upcoming Starfleet Academy project. He's a wonderful actor and he's done bad guy stuff before. (Big Fat Liar anyone? lol) And this got me thinking:

Who do trek fans consider their *favorite* villain in the Star Trek universe?

This is completely subjective and opinions will vary across the board, I'm sure. I look forward to seeing what you have to share.

For me? It's Gul Dukat.

The man is a complete egotistical psychopath. Arrogant and self-centered from the moment we meet him, up to the very end. And played brilliantly by Marc Alaimo. A bad guy you can't help but love to hate.

Who is your favorite Trek bad guy(s)?