Claude Frollo from The Hunchback of Notre Dame.
The realism of his motivations and the way he manipulates religion to achieve his goals always seemed far more frightening then any other monster of the week.
It's easy to remember that monsters aren't real, and that super villains with Tesla coils don't exist, but when it's a "normal" person in a position of power, that's just so much more difficult to push out of your mind. Yeah, I was a weird kid >_>