Black Sabbath is widely credited with inventing heavy metal, but they started as a blues-rock band called Earth. They changed their name after seeing people lined up to watch a horror movie. Bassist Geezer Butler noticed that people would pay good money to be scared by a film, specifically the 1963 Boris Karloff movie titled 'Black Sabbath.' He suggested that if people liked scary movies, maybe they would like 'scary music.' Guitarist Tony Iommi then wrote a dark, brooding riff using the 'tritone' (the musical interval known as 'the Devil's interval'), and Butler wrote lyrics about a terrifying encounter he had with a dark figure at the foot of his bed. This combination created a new genre of dark, heavy music that abandoned the 'flower power' themes of the late 1960s.