According to L. Ron Hubbard's Scientology, Xemu (often spelled “Xenu”) was a megabadguy who ruled the Earth 75 million years ago. I thought it would make an amusing, slightly mysterious sounding nom, rather in the vein of “Ximenes,” except a little sillier. Here's an old article from the Los Angeles Times, via the San Francisco Chronicle (used without permission) that explains a little more:

Los Angeles

Documents obtained by the Los Angeles Times show that the members of the Church of Scientology believe that mankind's ills were caused by an evil ruler named Xemu who lived 75 million years ago.

Scientologists have been trying to prevent the release of the documents, which they consider secret and sacred, and about 1500 church members crammed three floors of the Los Angeles County Courthouse on Monday, effectively blocking public access to documents.

Nevertheless, the Los Angeles Times had already obtained access to the documents, which were submitted as part of a civil case brought by former Scientologist Larry Wollersheim, before lawyers for the Scientologists requested they be sealed.

Wollersheim charges that the organization defrauded him by promising him higher intelligence and greater business success through Scientology courses that cost thousands of dollars.

In arguing to keep the court documents sealed, the church has told its members that it could be physically and spiritually harmful for them to learn about the upper levels of Scientology before they have mastered the preparatory courses. Scientology attorneys have argued that disclosure of the material violates the group's religious freedom.

Scientology is widely known for its use of “auditing”, a form of one-to-one counselling in which a lie-detector-like instrument called an E-meter is used to help a person erase negative experiences, supposedly freeing him to achieve his full potential.

The group bases its beliefs on the writings of L. Ron Hubbard, the reclusive science-fiction author who in the early 1950's published the best-seller Dianetics: the Modern Science of Mental Health.

What is rarely discussed, however, is Hubbard's secret teachings, which disclose his thoughts on why mankind has been plagued by problems through history, the topic of the disputed documents.

Generally, the documents suggest that a major cause of mankind's problems began 75 million years ago, when the planet Earth, then called Teegeeach, was part of a confederation of 90 planets under the leadership of a tyrannical ruler named Xemu. Then, as now, the materials state, the chief problem was overpopulation.

Xemu, the documents state, decided to take radical measures to overcome the overpopulation problem. Beings were captured on Earth and on other planets and flown to at least 10 volcanoes on Earth.

The documents state that H-bombs far more powerful than any in existence today were dropped on the volcanoes, destroying the people but freeing their spirits, called “thetans,” which attached themselves to one another in clusters.

After the nuclear explosions, according to the documents, the thetans were trapped in a compound of frozen alcohol and glycol and, during a 36-day period, Xemu “implanted” in them the seeds of aberrant behavior for generations to come. When people die, those clusters attach to to other humans and keep perpetuating themselves.

Before a Scientologist can learn about thetans and how to eradicate them, he must go through a progression of costly programs.

For hours on Monday, Scientologists swamped workers in the clerk's office with hundreds of requests to photocopy the documents.

Superior Court Judge Alfred L. Margolis, over strong objections, had issued an order Friday making the documents public at 9 a.m. Monday - on a first-come, first-served basis.

Scientologists, by snaking the line through three courthouse hallways, made sure that they were the only ones to buy copies of the materials.

Shortly before noon, Margolis, at the request of Scientology lawyers, resealed the materials, pending a hearing later this week.

Jeff Pomerantz, a Scientology spokesman, said the strategy was intended to “keep the materials secure … Religion is not supposed to be disseminated from the courtroom.”