Xenu (/ˈziːnuː/),[1][2][3] also called Xemu, was, according to Scientology founder L. Ron Hubbard, the dictator of the "Galactic Confederacy" who 75 million years ago brought billions[4][5] of his people to Earth (then known as "Teegeeack") in a DC-8-like spacecraft, 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]
This is also known as the OT-3 level in Scientology
https://en.wikipedia.org/wiki/Xenu