The World of Tiers is a series of science fiction novels by American writer Philip José Farmer. They are set within a series of artificially constructed universes, created and ruled by decadent beings who are genetically identical to humans, but regard themselves as superior, and are the inheritors of an advanced technology they no longer understand. This technology enables the "Lords" (or "Thoans", as described by Farmer in his introduction to a role-playing video game) to create novel lifeforms, and also to prevent aging or disease, making them effectively immortal. Their technology also allows them to create small artificial universes (see pocket universe), and the planets and stars within them, and modify the physical laws (e.g., changing the behavior of gravity) to create unusual or interesting phenomena within these universes. Instantaneous travel within and between these universes is achieved by the use of "gates" which seem to function as teleportation devices, or as a means of creating wormholes between different regions of spacetime. The overall series title comes from the main "pocket universe" featured in the books. This consists of a single planet with a green sky, shaped in the form of a huge stepped pyramid on five stages, with each stage being a disk or squat cylinder. A small sun and a single moon orbit around this planet (thus, in this universe geocentrism is a correct description of astronomical reality). There are no other stars or astronomical bodies. This world was created by a Lord named Jadawin. The overall storyline of the series follows the adventures of two people from Earth who independently discover gates into the World of Tiers. The earlier books focus on the character of Robert Wolff as he explores this world and tries to discover its secrets. From the third book onwards the action shifts to Paul Janus Finnegan (known as Kickaha, along with many other aliases), who is drawn into a battle between an ancient enemy of the Lords, and ultimately into the feuds between rival Lords as they try to take over each other's universes. A French-language roleplaying game, Thoan - Les Faiseurs d'Univers, inspired by the World of Tiers, was released in 1995. Source: Wikipedia (en)