Metal's obsession with downtuned riffage, thudding grooves and dark atmospherics all can be traced back to Black Sabbath. Emerging in the early '70s, the quartet warped acid rock and British blues into a radically original funereal vision. “Iron Man”, “Children of the Grave” and “God Is Dead?” anchor pummelling beats with Ozzy Osbourne's tortured cries and Tony Iommi's lurching fretwork. When the operatic Ronnie James Dio stepped in for Ozzy in the '80s, Sabbath didn't miss a beat, unleashing several killer records that blended their trademark doom with New Wave of British Heavy Metal-style speed and fury.