I have always been fascinated by some of the very questionable things that people believe, and more often than not it will include some of their religious beliefs. Scientologists are a grab bag of really weird shit. Oftentimes they will denounce any questions about a belief in 'Xenu' as "preposterous" or "nonsense".
"Xenu also spelled Xemu, was, according to the founder of Scientology L. Ron Hubbard, the dictator of the "Galactic Confederacy" who, 75 million years ago, brought billions of his people to Earth in a DC-8-like spacecraft, stacked them around volcanoes and killed them using hydrogen bombs. Official Scientology scriptures hold that the essences of these many people remained, and that they form around people in modern times, causing them spiritual harm.
Within the Church of Scientology, the Xenu story is part of the church's secret "Advanced Technology", considered a sacred and esoteric teaching, which is normally only revealed to members who have contributed large amounts of money. The church avoids mention of Xenu in public statements and has gone to considerable effort to maintain the story's confidentiality, including legal action on the grounds of copyright and trade secrecy. Officials of the Church of Scientology widely deny or try to hide the Xenu story. Despite this, much material on Xenu has leaked to the public via court documents, copies of Hubbard's notes, and the Internet. In commentary on the impact of the Xenu text, academic scholars have discussed and analyzed the writings by Hubbard and their place within Scientology within the contexts of science fiction, UFO religions, gnosticism and creation myth. ....."
The History Of Xenu - As Explained By L. Ron Hubbard