Like memorable protagonists, creating memorable antagonists is critical to your story–at least if you want to tell a good story.
The key to crafting a good villain is all how 3-dimensional he/she is–the villain isn’t simply bad to be bad. He’s bad for a reason, and readers need to understand what that reason is. Why does this person/creature choose to do what most of the world views as wrong?
On top of that, a 3-D villain will be somewhat sympathetic and possibly even a little heroic—he’s just on the “wrong side of the battle”. And we, the readers, understand why he’s bad, so although we may not agree with him, we do feel a bit sorry for him.
A compelling antagonist,like a compelling protagonist, has a desperate need and will do whatever it takes to achieve this goal.
More importantly, he has an understandable reason for wanting his goal. It may be a terrible reason and one we can’t sympathize with (such as a love of seeing someone else’s pain), but there IS a reason there (thanks again to Ilana for pointing this out).
For example, in the Harry Potter and the Half-Blood Prince, we start to see why Voldemort went from being a boy named Tom Riddle to a power-hungry, hateful monster…and we actually feel bad for the kid. We understand how he evolved into the Dark Lord, and we almost wish he would just throw in the towel and redeem himself. But alas, he does not.
Heck, even Professor Snape (who is an antagonist, but not a villain) has one heck of a backstory to explain his nasty behavior.
Now don’t get me wrong: sometimes, wanting World Domination for the sake of World Domination can work for a villain (see Star Wars or Lord of the Rings). But more often than not, if there’s a believable reason for the villain to want World Domination (see Harry Potter or The Native Star by M.K. Hobson), it will add a wonderful dimension to your story.
One of my favorite villains is from Sherwood Smith’s Inda. In this story, the heir to throne is a bully who makes his younger brother’s life a complete, tortuous hell. But there’s a reason he does this: he has an incapacitating stutter, he’s not good at reading or studying, and he is jealous of his younger brother’s scholarly skills. The King, their father, often praises the younger brother and not the bully. We know now why the bully wants to constantly make his younger brother look bad, why he hates scholarly people, and why he prefers to use his fists rather than his voice to make a point. We feel bad for the bully, even if we don’t want him to win.
Now you tell me: what do YOU think makes for a good villain or antagonist?