What makes a worthy villain?
[Disclaimer: After consulting with Captain REX via MSN, I have concluded that this forum is da spot for this thread entitled "What makes a villain?". So, basically, for those of you who might say "Oi, dis belongs in teh movies section!!1!", REX will bring down the wrath of hell upon your immortal souls.]
As someone who enjoys a good movie, I find myself agreeing with Roger Ebert's sentiment that "a movie is only good as its villain" since they are ultimately the characters who drive the plot and likely serve as catalysts for the protagonists; I also happened to finish rereading Deathly Hallows today, and upon my third read, I consider Voldemort to be a lackluster villain. Despite his reputed intellect and charisma, he's portrayed as remarkably incompetent.
Basically, I'm curious as to what you all think makes a worthy villain.
Edit: This applies to all genres: movies, video games, and literature.