From the Wikipedia:
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. These events are known as “Incident II” or “The Wall of Fire”, and the traumatic memories associated with them as the R6 implant. Scientology founder L. Ron Hubbard detailed the story in Operating Thetan level III in 1967, famously warning that R6 was “calculated to kill (by pneumonia etc) anyone who attempts to solve it.” Much controversy between the Church of Scientology and its critics has focused on Xenu. The Church avoids making mention of Xenu in public statements and has gone to considerable effort to maintain the story’s confidentiality, including legal action on both copyright and trade secrecy grounds. Critics claim that revealing the story is in the public interest, given the high prices charged for OT III. The Xenu story prompted the use of the volcano as a Scientology symbol.
Although I’m sure this is the way the Romans felt when they heard that some whack-job from some backwater had proclaimed himself God’s son and had been resurrected after his death by capital punishment.