Was Hitler insane, or just evil?

I’ve always thought Hitler must have been seriously ill, but my family all disagree with me and say he’s just plain evil. And after watching Der Untergang (Downfall) I’m beginning to question if he was just rotten after all.

What do you think? Could the death of millions of innocent people be down to just one ‘normal’ but very evil man? Or would you have to be seriously mentally ill to even think of killing that many people for such stupid reasons?

If you do believe he was mentally ill, which mental illness do you think he had?