Brooklyn Vegan points out that Martin Eric Ain, longtime bassist for the influential Swiss underground metal greats Celtic Frost, died on Saturday after suffering from a heart attack. Ain was 50.

Ain first joined forces with future Celtic Frost frontman Tom Gabriel Fischer (then known as Tom G. Warrior) in 1981, in the pre-Celtic Frost band Hellhammer. Hellhammer became a sort of underground word-of-mouth sensation among metalheads in the early ’80s, and their fast, murky sound would go on to help spark the grindcore, death metal, and black metal scenes that would follow.

Ain remained with Fischer in Celtic Frost, the band they formed in 1984, after Hellhammer’s demise. Celtic Frost also made dark, extreme metal, but their sound was more abstract. They would play around with tape loops, drum machines, and funk and industrial textures, and they stand today as one of the most adventurous and underrated metal bands of their era. Two of their albums, 1984’s To Mega Therion and 1987’s Into The Pandemonium, remain absolute classics of the genre. (A lot of people also rep for their debut, 1984’s Morbid Tales.)

Ain and Fischer had a tempestuous relationship, and Ain left and rejoined the band several times. Ain wasn’t in the band, for instance, when they released 1988’s misbegotten glam metal experiment Cold Lake, but he rejoined afterward. Celtic Frost broke up in 1993, and Ain went onto open up a bar in Zurich. But Ain teamed up again with Fischer to reform Celtic Frost in 2001. They released one last absolute stunner of an album, 2006’s Monotheist, before breaking up again in 2008. I never saw them in their ’80s peak, but their mid-’00s live shows were something to behold. Also, I interviewed Fischer and Ain together in 2006, and Ain struck me as being a profoundly good dude. Below, watch a couple of Celtic Frost videos.