The story of Xenu is covered in OT III, part of Scientology's secret "Advanced Technology" doctrines taught only to advanced members who have undergone many expensive hours of auditing and reached the state of Clear. It is described in more detail in the accompanying confidential "Assists" lecture of October 3, 1968 and is dramatized in Revolt in the Stars (a screenplay written by L. Ron Hubbard in 1977).
Hubbard wrote that seventy-five million years ago, Xenu was the ruler of a Galactic Confederacy which consisted of 26 stars and 76 planets including Earth, which was then known as "Teegeeack". The planets were overpopulated, each having 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. Hubbard described the scene in his film script, Revolt in the Stars:
Simultaneously, the planted charges erupted. Atomic blasts ballooned from the craters of Loa, Vesuvius, Shasta, Washington, Fujiyama, Etna, and many, many others. Arching higher and higher, up and outwards, towering clouds mushroomed, shot through with flashes of flame, waste and fission. Great winds raced tumultuously across the face of Earth, spreading tales of destruction...
– L. Ron Hubbard, Revolt in the Stars
The now-disembodied victims' souls, which Hubbard 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 Hubbard 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, with Hubbard specifically attributing Roman Catholicism and the image of the Crucifixion to the influence of Xenu. The two "implant stations" cited by Hubbard 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 Scientologists 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 a mountain, where he was imprisoned forever by a force field powered by an eternal battery. Although the location of Xenu is sometimes said to be the Pyrenees on Earth, this is actually the location Hubbard gave 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.
The cost of learning these secrets from the Church of Scientology was 3,830 British pounds, or 6,500 US dollars, in 1988. This is additional to the cost of the prior courses which are necessary to be eligible for OT III. Belief in Xenu and body thetans is a requirement for a Scientologist to progress further along the Bridge to Total Freedom.
Within Scientology, the Xenu story is referred to as "The Wall of Fire" or "Incident II". Hubbard attached tremendous importance to it, saying that it constituted "the secrets of a disaster which resulted in the decay of life as we know it in this sector of the galaxy". The broad outlines of the story—that 75 million years ago a great catastrophe happened in this sector of the galaxy which caused profoundly negative effects for everyone since then—are publicly admitted to lower-level Scientologists. However, the details are kept strictly confidential, at least within the Church.
The OT III document describes how Hubbard entered the Wall of Fire but emerged alive, "probably the only one ever to do so in 75,000,000 years". He first publicly announced his "breakthrough" in Ron's Journal 67 (RJ67), a taped lecture Hubbard recorded on September 20, 1967 to be sent to all members of the Church. According to Hubbard, his research was achieved at the cost of a broken back, knee and arm. OT III contains a warning that the R6 implant is "calculated to kill (by pneumonia etc) anyone who attempts to solve it." In RJ67, Hubbard then alludes to the devastating effect of Xenu's genocide:
“ And it is very true that a great catastrophe occurred on this planet and in the other 75 planets which formed this [Galactic] Confederacy 75 million years ago. It has since that time been a desert, and it has been the lot of just a handful to try to push its technology up to a level where someone might adventure forward, penetrate the catastrophe, and undo it. We're well on our way to making this occur. ”
OT III also deals with Incident I, set four quadrillion years ago (or roughly 300,000 times longer than the current scientifically accepted value for the age of the universe).