Agreed. Superman without the superpowers, or perhaps the Non-Invisible Man. Or that novel about the time non-existent Martians never invaded the Earth. That was a classic. I remember the film that wasn't made about that; I remember not going to see it.
At the age of five, Skagra decided emphatically that God did not exist. This revelation tends to make most people in the universe who have it react in one of two ways - with relief or with despair. Only Skagra responded to it by thinking, 'Wait a second. That means there's a situation vacant.'