When he was 17 years old, a young guitarist, born Frank Anthony Iommi, sliced the tips off two of his fingers while working at a sheet metal factory in Birmingham. The story goes that he was so determined to keep playing guitar, he fashioned prosthetic tips out of melted plastic bottles and detuned his guitar by a minor third because the looser strings were easier to play. Three years later, that ominous detuned tone would form the backbone of Black Sabbath’s sound. And it happened almost entirely by accident. It’s not that Black Sabbath invented heavy metal. By the end of the 1960s, genre co-pioneers Deep Purple and Led Zeppelin had already begun unleashing distortion, riffs, and solos on a generation still enamored with folk and early psychedelia. But it took a different kind of heaviness—the kind inspired by horror films, the occult, and a bleak working-class upbringing in Aston, Birmingham—to give heavy metal its true form. Enter four twenty-something blokes and the debut album they recorded in 12 hours. Much like the horror genre (the band name itself was stolen from a 1963 Italian anthology by “Master of the Macabre” Mario Bava), these songs were generally designed to incite fear, terror, suspense, excitement. First, the scene is set: a dark and stormy night. Heavy rain, thunder, and creepy church bells lay the foundation of “Black Sabbath” (the first song on Black Sabbath’s first album, Black Sabbath). It’s almost 40 seconds before the guitar riff strikes. Soon, Ozzy Osbourne starts singing about a mysterious “figure in black” pointing and staring at him—the lyrics were inspired by a vision bassist Geezer Butler had experienced in his room, then painted completely black, decorated with occultist books and satanic images. A few lines later comes Osbourne’s very first ungodly howl: “Oh, no, no, please, God help me.” It’s a song so intense and demonic, it not only terrified and intrigued millions, it instantly created the doom metal subgenre and led to countless Sabbath-worshipper attempts to emulate its impact ever since. Despite the hasty recording session, an incredible level of creativity went into the stories behind these songs. Led Zeppelin might be the biggest Tolkien fanatics in rock, but Iommi, who was reading Lord of the Rings at the time, found inspiration for “The Wizard” in Gandalf: “Evil power disappears, demons worry when the wizard is near/He turns tears into joy, everyone's happy when the wizard walks by.” “Behind the Wall of Sleep” pays homage to H.P. Lovecraft, and “N.I.B.” is a twisted, Cream-inspired love song from the perspective of Lucifer himself. Black Sabbath was, appropriately, released on Friday the 13th in February 1970, and, despite being panned by critics, became so successful that they returned to the studio just four months later to record Paranoid.