Xenu is the multi-Galactic dictator of the "Galactic Confederacy" which consisted of 26 stars and 76 planets who, 75 million years ago, brought billions of his own people to Earth (which was then known as "Teegeeack") in a DC-8-like spacecraft, stacked them around volcanoes and killed them using hydrogen bombs. Some believe these were deserving insurrectionists to his righteous war for power, some think it was to control the population, others think it was just for a lark.
he was so perfect in his evil that not only were the rebellious thetans destroyed in a painful volcanification process, but their ineffectual ghosts haunted the bystanding human victims for millions of years thereafter while Speed Xenu drove around the galaxy getting drunk and having anonymous unprotected sex at space jacuzzi parties.
Any doctrine stating that Speed Xenu, Intergalactic Space Pirate, stuck around to torture or beguile the ghost and non-ghost populations of Earth is utter disinformation by the corrupted Church of Scientology, which is now a dark cult dedicated to calling back this evil Lord of Space.
Named 'Speed' for his dynastic family lineage of space dragster racing, but deciding to leave the family long ago so as not to bring them shame, he became the greatest Space Pirate in all of history. His acts of cruelty and viciousness were so effective, he had soon carved out a crescent of political power amongst evil solar systems, finally conquering his entire Galaxy. Within a million years, the neighboring galaxies fell as well.
Speed Xenu never forgot his pirate roots, and always has a good time all the time. He never bothered returning to Earth, since it was merely useful as a trash planet. If he were to return either by chance or curiosity or less likely nostalgia, we would all surely burn.
Xenu's Empire's growth was halted by the growth of other powerful Empires, such as the Maypo Galaxy.
Xenu loves psychology. Just loves it.