Creating an Interesting Villain

Readers tend to prefer characters who are at least somewhat sympathetic. In the case of villains, sympathetic is perhaps the wrong word: Understandable is better. Interesting is best of all. The bad guy whose sole reason for blowing up the galaxy is because that's what bad guys do won't be around for a sequel. Even Darth Vader needs motivation. It changes him from a cardboard cutout villain to a three-dimensional character, and three dimensions are far more interesting than two.

Ester M. Friesner in How to Write Funny, John B. Kachuba, editor, 2001