I saw the documentary in a spirit of curiosity rather than fandom – and was won over by the visceral thrill of the band’s sound.

Soundgarden frontman Chris Cornell always had a wide range of influences, but one hard rock band stuck out to him more than any other.

It was in early 1969, after a change of name from The Polka Tulk Blues Band to Earth, that Iommi heard the first Led Zeppelin album and vowed to make music that was, in his words, “even heavier”.