What makes a villian memorable?

So you're writing about the eternal struggle between good and evil; you've got a strong plot and a charismatic hero/ine; now all you need is a good villain.

So what makes a villian memorable?

I'm a fan of villains who are real people and who have enough charisma that you'd love to be their friend if it wasn't for their unfortunate addiction to decapitating their enemies.

To keep the character real this villain has to have some reason for doing what they do.

I'm a fan of the old saying: "Heroes have flaws, villains have reasons" as a way of distinguishing the motivation of the two poles your story hangs on

If you want to make your villain first rate then take a look at this article on what makes a good villain in a film

Here's a sample of the article to whet your appetite:

"Villainy is, in essence, behavior inspired by values which are inscrutable, aversive or repugnant to us in our more civilized moments of reflection. We console ourselves with the thought that villains are twisted aliens. Consequently, what makes a villain truly interesting is to glimpse his or her non-alien, distinctly human rationalization of these values, much as Gordon Gekko's terse philosophizing provided in ‘Wall Street’. But, was Gekko a villain to Gekko?"