Xenu was 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.
Xenu was the ruler of a Galactic Confederacy 75 million years ago, which consisted of 26 stars and 76 planets including Earth, which was then known as "Teegeeack". The planets were overpopulated, with an average population of 178 billion. The Galactic Confederacy's civilization was comparable to our own, with aliens "walking around in clothes which looked very remarkably like the clothes they wear this very minute" and using cars, trains and boats looking exactly the same as those "circa 1950, 1960" on Earth.
Xenu was about to be deposed from power, so he devised a plot to eliminate the excess population from his dominions. With the assistance of psychiatrists, he summoned billions of his citizens together under the pretense of income tax inspections, then paralyzed them and froze them in a mixture of alcohol and glycol to capture their souls. The kidnapped populace was loaded into spacecraft for transport to the site of extermination, the planet of Teegeeack (Earth). The appearance of these spacecraft would later be subconsciously expressed in the design of the Douglas DC-8, the only difference being: "the DC8 had fans, propellers on it and the space plane didn't". When they had reached Teegeeack/Earth, the paralyzed citizens were unloaded around the bases of volcanoes across the planet. Hydrogen bombs were then lowered into the volcanoes and detonated simultaneously. Only a few aliens' physical bodies survived.
The now-disembodied victims' souls, called thetans, were blown into the air by the blast. They were captured by Xenu's forces using an "electronic ribbon" ("which also was a type of standing wave") and sucked into "vacuum zones" around the world. The hundreds of billions of captured thetans were taken to a type of cinema, where they were forced to watch a "three-D, super colossal motion picture" for thirty-six days. This implanted what is termed "various misleading data"' (collectively termed the R6 implant) into the memories of the hapless thetans, "which has to do with God, the Devil, space opera, et cetera". This included all world religions, specifically attributing Roman Catholicism and the image of the Crucifixion to the influence of Xenu. The two "implant stations" cited were said to have been located on Hawaii and Las Palmas in the Canary Islands.
In addition to implanting new beliefs in the thetans, the images deprived them of their sense of personal identity. When the thetans left the projection areas, they started to cluster together in groups of a few thousand, having lost the ability to differentiate between each other. Each cluster of thetans gathered into one of the few remaining bodies that survived the explosion. These became what are known as body thetans, which are said to be still clinging to and adversely affecting everyone except those who have performed the necessary steps to remove them.
A government faction known as the Loyal Officers finally overthrew Xenu and his renegades, and locked him away in "an electronic mountain trap" from which he still has not escaped. Although the location of Xenu is sometimes said to be the Pyrenees on Earth, this is actually the location given elsewhere for an ancient "Martian report station". Teegeeack/Earth was subsequently abandoned by the Galactic Confederacy and remains a pariah "prison planet" to this day, although it has suffered repeatedly from incursions by alien "Invader Forces" since that time.
In 1988, the cost of learning these secrets was $6,500. This is in addition to the cost of the prior courses which are necessary to be eligible for OT III, which is often well over US$100,000. Belief in Xenu and body thetans is a requirement to progress further along the Bridge to Total Freedom. Those who do not experience the benefits of the OT III course are expected to take it (and pay for it) again.
This is the doctrine for Scientology. While writing it, Hubbard, the founder of Scientology and science fiction writer, wrote to his wife saying, “I'm drinking lots of rum and popping pinks and greys."
And thus not only answers another question I’ve carried in my head, but given me a hearty laugh, and have subsequently filed it under “kooky cults” with a few other religions.