Tony Iommi

The most consequential industrial accident in music history: a Birmingham sheet-metal press, a seventeen-year-old’s last day at work, and two fingertips that never came back. Everything Tony Iommi did next — the homemade thimbles, the lighter strings, the downtuning — was engineering, not aesthetics. The aesthetics came out anyway, and they were called heavy metal.

Iommi’s file in the lab is the purest case study we have of a constraint inventing a genre. Start with the factory; the riffs explain themselves from there.