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. Sabbath enjoyed an unrivaled commercial run in the '70s, essentially defining the heavy metal genre with landmark albums like Paranoid and Master of Reality. In addition to his work with Blac...