Xenu is the central character in the creation story told by Scientology founder L. Ron Hubbard. Seventy-five million years ago, Xenu, the dictator of the Galactic Confederacy, brought billions of people to the planet of Teegeeack (Earth) in an aircraft the size of a passenger jet. Upon arrival, Xenu put all of his people under volcanoes and blew them up with atomic bombs. The essences of these people remain on Earth and do harm to modern humans.
Although the Church of Scientology has gone to great lengths to prevent this story from being publicly known, its secrecy has been breached via court documents and the Internet. There is no empirical evidence to substantiate the Xenu story. It is no more plausible than any other work of science fiction. A passenger jet cannot reasonably be argued to have the capacity to transport billions of people. No other literature outside of Scientology is known to speak of Xenu.
The creation myth of Scientology and the character of Xenu are works of science fiction. No empirical evidence supports the story and its details are implausible.