[Johnny1A.2]

Helmuth, from E.E. Smith's Galactic Patrol. Thoroughly bad, but in an efficient, effective, intelligent way. He's the sort of man who, if he'd grown up in a sane society, would be a hero. He's actually a more dangerous opponent than many of the later, higher ranking Boskonians Kimball Kinnison would defeat, it makes me wonder if the Arisians didn't arrange for Helmuth to go down early because he was too dangerous to be allowed to gain more power.

John Marcone, from The Dresden Files. A mobster, but one with a few redeeming features (not many, he's definitely still a bad guy), but like Helmuth, intelligent, capable, and efficient. Totally unsentimental, doesn't waste time monologuing or with meaningless chit-chat, won't hesitate to shoot you in cold blood if you give him backtalk, but not sadistic about it.

Actually, he and Helmuth have some traits in common.

Baron Vladimir Harkonnen. Far more personally corrupt and perverse than either of the previous two, but still dangerously intelligent and effective. His effectiveness is somewhat reduced by his personal corruption, though.

Arguably Feanor, from Tolkien's stories. He's a classic case of 'madness makes the villain', but also a good exemplar of just that sort of villainy, driven by passion out of control of conscience and humility.

Which is a tendency. The most effective villains tend to be the ones who still have some good in them. As corruption proceeds, evil tends to be self-defeating because the very behaviors it produces work against itself.