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Black Sabbath’s self-titled debut on Vertigo established heavy metal’s sonic blueprint—a seismic collision of Iommi’s downtuned riffs, Ozzy’s haunted vocals, and Ward’s thunderous drums that turned blues-rock into something darker and heavier. Released in 1968, the album’s opening title track became the genre’s founding statement, its tritone interval and crushing distortion defining what heavy metal could be. This is the sound that changed everything.