A great 'Villain'? Tim.
A poor, lonely man in search of a princess who was captured by a great evil. Only... It's not that simple, is it?
What makes him a great villain, you ask? The fact that he's not aware he is one. Evil is almost never committed for evil's sake. No one destroys the world just because it would be particularly mean. There's always a reason behind it, generally fueled by some sort of madness.
There are two kinds of great evils. Evil stemming from pure insanity and evil stemming from warped reason. The latter is far worse to fight. Sure, the crazies that just want to let the world burn are certainly more frightening at first glance, but the power of a misguided voice dwarfs that of a single madman in the long run. After all, you can shoot a crazy man. But a misguided man will have hundreds, thousands, or even millions of followers under his flag who are all too eager to carry on his legacy. In this way, even after his swath of destruction and moral decay is technically ended, the death toll will doubtless tick on. And that's what makes misguided villains so terrifying: As long as the idea makes sense to one person, the founder of the thought is never truly dead.
Hitler was not a saturday morning cartoon villain, plotting the holocaust because it would be seen as horrible and devious. He did it because he truly thought the world would be a better place. This did stem from his hatred of jews, yes. But that was exactly what misguided him into thinking he was doing the world a service. Similarly, Adam Monroe thought that weeding out a greater portion of the population would make the world a better place. It's now
how a villain acts that makes them great (though it certainly helps), but
why. From a literary and theatrical point of view, that is.