The Mad Goblin (Secrets of the Nine #3 - Wold Newton Parallel Universe) by Philip Jose Farmer
They were known simply as the Nine - grim and ancient rulers who thirty thousand years ago had discovered the key to eternal life and ever since had secretly held the world in thrall. Once, Doc Caliban had been their servant and had shared their secrets. Now, appalled by their tyranny, Caliban sets out on the trail of the deadliest of the Nine: the mad goblin Iwaldi, the very incarnation of Evil...