There's nothing quite like an encyclopedia for coldly detailing just how loony loons can be:
In Scientology doctrine, Xenu is a galactic ruler who, 75 million years ago, brought billions of people to Earth, stacked them around volcanoes, and blew them up with hydrogen bombs. Their souls then clustered together and stuck to the bodies of the living, and continue to cause people problems today. These events are known to Scientologists as "Incident II," and the traumatic memories associated with them as The Wall of Fire or the R6 implant. L. Ron Hubbard, founder of Scientology, detailed the story in Operating Thetan level III (OT III) in 1967, famously warning that R6 was "calculated to kill (by pneumonia etc) anyone who attempts to solve it." The Xenu story was the start of the use of the volcano as a common symbol of Scientology and Dianetics from 1968 to the present day.