Mr. Crowley is one of two singles released from the Blizzard of Ozz album, with Crazy Train being the first. The song was inspired by a book about Aleister Crowley which Osbourne had read and a deck of tarot cards that were found in the studio as recording of the album was commencing. Crowley was an English occultist and ceremonial magician who had founded the Thelemite religion in the early 20th century.
The video game Fallout 3 uses the lyrics to the song in its walkthrough of You Gotta Shoot 'em in the Head. The game also features a ghoulish character named "Mister Crowley".