Xenu (/ˈzi:nu:/),[1][2][3] also called Xemu, was, according to Scientology founder L. Ron Hubbard, the dictator of the "Galactic Confederacy" who brought billions[4][5] of his people to Earth (then known as "Teegeeack") in DC-8-like spacecraft 75 million years ago, stacked them around volcanoes, and killed them with hydrogen bombs. Official Scientology scriptures hold that the thetans (immortal spirits) of these aliens adhere to humans, causing spiritual harm.[1][6]

src: https://en.wikipedia.org/wiki/Xenu