Xenu is, according to widespread belief, the Galactic Warlord who infested our planet with aliens . Luckily, L. Ron Hubbard found this out and started a movement to dispel these pesky creatures. While there is no official admission from the Scientolgy group that such a thing exists, there are several websites that provide the information based on public records, lawsuits, and alleged Scientologists who abandon the group and start spilling information.

Here is the alleged OT3 description of Xenu:

The head of the Galactic Federation (76 planets around larger stars visible from here) (founded 95,000,000 years ago, very space opera) solved overpopulation (250 billion or so per planet, 178 billion on average) by mass implanting. He caused people to be brought to Teegeeack (Earth) and put an H-bomb on the principal volcanos (Incident II) and then the Pacific area ones were taken in boxes to Hawaii and the Atlantic ones to Las Palmas and there "packaged."

His name was Xenu. He used renegades. Various misleading data by means of circuits etc. was placed in the implants.

When through with his crime loyal officers (to the people) captured him after six years of battle and put him in an electronic mountain trap where he still is. "They" are gone. The place (Confederation) has since been a desert. The length and brutality of it all was such that this Confederation never recovered. The implant is calculated to kill (by pneumonia etc) anyone who attempts to solve it. This liability has been dispensed with by my tech development.

Supposedly Xenu solved his population problems by bringing these beings set to be culled here and implanted them with false memories. Then, he destroyed them and captured their souls. A few souls got away (70 or 80 billion, something like that) and now plague us humans. Why this information is not freely shared with the public is anybody's guess. Christians, Catholics, and nearly every other religion, aside from a few cult-like spinoofs, share religious information to the point of excess. But then again, who doesn't want to be in a secret club?

This information is not presented as any claim against Scientology, merely as an example of information that can be gathered on the internet should one become bored.