Black Sabbath's Tony Iommi is one of only two guitarists (the other being Led Zeppelin's Jimmy Page) who can take full credit for pioneering the mammoth riffs of heavy metal. As the primary composer, guitar player, and sole constant member of Black Sabbath, Iommi carved out a dark, bluesy, and distinctive style - he tuned his guitar a half-step down to accommodate a grisly finger injury.