In my current WIP, I realized I needed to take a step back and evaluate my antagonists. They weren't EVIL enough to be evil villains.
I have a soft spot for villains who are flawed, human, and have strong, logical motives. I go crazy when I read a story with a villain who is 'pure evil'. To make an analogy, it's the difference between Draco Malfoy and Lord Voldemort in Harry Potter. Draco is misguided and corruptible, and much of his motivation seems to stem from a need to impress his friends and uphold his family name.
But Voldemort -- *sigh* -- does he actually have a motive? I always wondered what Voldemort's endgame was.
I've rid the world of mudbloods and muggles. Time for my vacay!
In my mind, there is no such thing as 'pure evil' or 'pure good'. It's fun to explore all of the shades of grey in this spectrum, to more fully understand how a character came to a certain point in his life, and how he can justify his actions. This is actually one of my favorite parts about Stephen King's THE STAND. There's a whole range of 'goodness' and 'evilness' depicted -- we have Harold, who is weak and corrupted by temptation; Larry, whose character arc is all about redemption; and Nadine, who feels compelled to fulfill her destiny, yet ultimately finds the strength to rebel.
So what makes a great villain? For me, it comes down to three things:
1. The villain has to have some kind of power. He doesn't have to be all powerful, but he does need to be powerful enough to be a serious threat to the MC. The villain must be a true match for our protagonists, a 'great and worthy opponent'.
2. The villain's motives must be logical -- he's a character, not a plot device. The reader should clearly understand why the villain behaves the way he does. Why does a killer go on a murderous rampage? Why does an evil Senator threaten to take over the Empire? Even if the logic is twisted, a great villain has a game plan. Ideally, one they do not share with the hero.
3. Even if the villain's motives are logical, there must be an element of unpredictability. How far will our villain go to meet her goals? Our heroine might know someone that she secretly wishes was dead, but the villain actually pops his enemies. Our hero might be tempted to do something immoral to meet a goal, but our villain just goes for it.
Of course, a monocle and Persian cat don't hurt, either.