Terrence Michael Joseph Butler, better known as Black Sabbath’s groundbreaking bassist Geezer Butler, was born on July 17, 1949 in Birmingham, England.

Butler originally had aspirations of being a rock guitarist, but that changed when he swapped six strings for four upon joining Black Sabbath when they were first known as Polka Tulk. As the band’s sonic shift evolved from blues to the darker, riff-intensive sound that would ultimately spawn the entirety of heavy metal, he proved to be Sabbath’s oddball as a psychedelic-loving hippie who had an obsession with the occult.

His foundation-cracking bass lines created a titanic wall of sound when played beneath Tony Iommi’s lumbering riffs. His progression was remarkable for a man who had only just begun to play the instrument and Butler quickly moved with Bill Ward’s eccentric drumming, adding fluid splashes of fills while taking full control elsewhere (“N.I.B.” anyone?), inspiring legions of heavy metal bass players over the next half a century.

It’s always those with the most unorthodox approach who tend to stand out the most. While Butler’s playing can certainly carry that label in hindsight, it’s not as if he was breaking the rules — they simply didn’t exist for what Sabbath were doing as he unknowingly laid the groundwork for 50 years of bass players to come..