The alarming, dissonant guitar groan that kicks off “Iron Man,” eventually cohering into a primal five-note riff, struck lead singer Ozzy Osbourne as evoking “a big iron bloke walking about.” So it’s all the more surprising that Black Sabbath apparently had neither the Marvel comic hero nor Ted Hughes’ Iron Giant in mind when they pounded together this foundational slab of heavy metal, about a time-traveling seer who turns to steel and plots revenge. Even today, “Iron Man” seems pulled from ancient wreckage — an industrial artifact of the rubble-strewn steel towns of the English Midlands that stood in stark, sooty contrast to sunnier ’70s hard rock. (Fun fact: Ozzy couldn’t come up with a melody, so he just sang along with the guitar.)
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