The Death Gate Cycle
The Death Gate Cycle is a seven part series of fantasy novels by Margeret Weis and Tracy Hickman. The story follows the conflict between two very powerful races, the Sartan and the Patryns. These two races are branches of hunmans, changed following a nuclear holocaust. Hundreds of years before the events of the novels, the Sartans attempted to end the conflict between the two races by sundering the world into four elemental realms and then creating a fifth as a prison for the Patryn, called the Labyrinth.
The Sartan seperated to look after each realm but soon lost contact with each other, and dissapeared. Centuries pass and a Patryn called Xar manages to escape from the Labyrinth, returning to resucue others. He then began to learn how to reach the other worlds and began to plan their downfall. Escaping from the Labryrinth is the Patryn Haplo, who is sent by Xar to scout the other worlds, sow the seeds of chaos, and undermine the cultures in preparation of the invasion.