Sourcery : a novel of Discworld
(Book)

Rincewind, the world's most inept wizard, magically returns after falling off the edge of the world, this time carrying the Luggage, in a humorous fantasy of magic and mayhem. A sourcerer is born--a wizard so powerful that by comparison all other magic is just mucking about in pointy hats--and his very existence brings the Discworld to the very verge of all-out thaumaturgical war. All that stands in its way is Rincewind, the failed magician, who wants to save the world, or at least the part of it which contains him.