Xenu

Xenu ( ), also called Xemu, is a figure in the Church of Scientology's secret "Advanced Technology", an esoteric teaching held sacred by adherents. According to the "Technology", Xenu was the extraterrestrial ruler of a "Galactic Confederacy" who brought billions of his people to Earth (then known as "Teegeeack") in a DC-8-like spacecraft 75 million years ago, stacked them around volcanoes, and killed them with hydrogen bombs. Official Scientology scriptures hold that the thetans (immortal spirits) of these aliens adhere to humans, causing spiritual harm.

These events are known within Scientology as "Incident II", and the traumatic memories associated with them as "The Wall of Fire" or "R6 implant". The narrative of Xenu is part of Scientologist teachings about extraterrestrial civilizations and alien interventions in earthly events, collectively described as "space opera" by L. Ron Hubbard. Hubbard detailed the story in Operating Thetan level III (OT III) in 1967, warning that the "R6 implant" (past trauma) was "calculated to kill (by pneumonia, etc.) anyone who attempts to solve it".