Rogue Trader: Season One
A Psyker is an individual of any intelligent species in the Warhammer 40,000 universe who possesses some degree of psychic ability or powers. Psychic powers are sometimes referred to as sorcery in the Imperium of Man and among the Eldar, particularly when such powers are used in such a way that they show no regard for the dangers they may spawn for others or they are used in pursuit of the agenda of the Chaos Gods. Psykers draw their powers from the dimensional realm known as the Immaterium or the Warp that underlies four-dimensional realspace and is the source of all psychic energy in the universe. As such, psykers, particularly human psykers whose minds are far less disciplined than their Eldar counterparts, are often in danger of possession by the daemonic entities of the Warp, insanity and ultimate corruption by the Ruinous Powers of Chaos.