Black Sabbath's first two releases, Black Sabbath and Paranoid, were more than groundbreaking, they were earth-shattering, exposing the public to a brutal new form of noise pollution termed heavy metal. But it was the band's third album, Master of Reality, that cemented the group as blackened wizards of doom and gloom. Just listen to the echoing cough and sludgy guitar riff of the opening track "Sweet Leaf" and compare it to anything that existed at the time. Not only were Black Sabbath heavier than Deep Purple or Vanilla Fudge, they were also more experimental and controversial, exploring themes of darkness, drugs, and depravity that others dared not address. The heaviest and most influential disc of Black Sabbath's career, Master of Reality featured proto-metal sludge like "Children of the Grave" and "After Forever," which served as a blueprint for a legion of musicians including '90s Nirvana, Soundgarden, and Smashing Pumpkins.