Behind the Walls of Terra by Philip Jose Farmer
Paul Janus Finnegan was called Kickaha on the artificial universes created by that always fueding super-race known as the Lords. Though he was a mortal Earthman, he had managed to survive every intrigue, war, test and opponent they could devise.But it was when he found his way back to his own world that Kickaha faced the greatest dangers of his adventure-filled career. For he knew the secrets of the powers that moved the cosmos, and this made him a threat -- a target of the terrible hidden forces contending for this very universe.
