Bob Heil was a massively important person in music history. I really don't know how well known he is outside of St. Louis, but he's revered here.
He was a tech nerd who loved tinkering with sound systems, which was a hobby he used in conjunction with his gig as the organist at the Fox Theater in St. Louis. In 1970, the Grateful Dead were on tour when their soundman Ousley had to vamoose right before their show in StL due to pending legal actions due to his slightly less legal gig manufacturing LSD. Left without a sound guy, Jerry Garcia took the advice of a local and called up Heil asking if he could fill in at the last minute. Heil showed up with the sound system he'd been tinkering with, which then blew the Dead's minds even more than acid by providing them with a sound system that was louder than anything they'd used before but without distortion. Heil ended up landing a much more lucrative job than organist at a theater.
Word got around that the Grateful Dead was managing to get as loud as hell without the sound turning into complete sludge, and soon Pete Townshend came calling, and Heil became an essential partner to the Who, helping them achieve their Guinness World Record for being the loudest band ever at that time and working with Townshend to achieve his vision for
Quadrophenia.
Watch live videos of Beatles stadium shows being completely drowned out by screaming teenaged girls.for life before Heil.
Aside from completely revolutionizing concert sound, Heil's other main invention was the Talk Box, beloved by Joe Walsh and Peter Frampton.