Now, we ARE talking about someone/something that has made a conscious decision to be evil, right? No entities that are just going about their business and get labeled "evil" by the protagonist/s of the Space Saga?

I gotta go with my man Scorpius from Farscape...slimy, mind invading half-breed creep that you just can't seem to kill.

I gotta give first runner up (and Miss Congenialty) to one of the originals, though: Ming The Merciless....that bastard!

Not sure if The Master from Dr. Who counts but, boy...talk about a dude that does not age gracefully...ever since his Roger Delgado incarnation (who was simply wicked for the sake of pure wickedness) it's been downhill ever since...

Best

AA