According to the band, the song was inspired by an experience that bassist Geezer Butler had in the days of Earth. Butler had recently become obsessed with the occult,so he painted his apartment matte black and placed several inverted crucifixes and pictures of Satan on the walls. Ozzy Osbourne gave Butler a black occult book as a gift. It was written in Latin and decorated with numerous pictures of Satan. Butler read the book and then placed it on a shelf beside his bed before going to sleep. When he woke up, he claims he saw a large black figure standing at the end of his bed, staring at him. The figure vanished and Butler ran to the shelf where he had placed the book earlier, but the book was gone. Butler related this story to Osbourne, who then wrote the lyrics to the song based on Butler's experience. The song starts with the lyrics: