Martin Eric Stricker was 16 when he and his friend Tom Gabriel Fischer formed Hellhammer. They were teenagers in Nürensdorf, a town outside Zurich, Switzerland that had nothing going on at all, the perfect environment to inspire intelligent, creative teenage boys to make as furious a noise as they could and blast all the bad shit out of their own heads. Fischer, who called himself Satanic Slaughter and later Tom G. Warrior, was fueled by deep internal angst, a horrific childhood, and a fixation on the dark side of the human spirit. Stricker, who called himself Slayed Necros before taking the surname Ain, was looking even deeper.

Even his stage name was meaningful; as he told Decibel’s J. Bennett in a 2006 interview, “I was starting to read about occultism, religion, philosophy. and systems of practical magic, like the Golden Dawn as taught by Aleister Crowley. I also came across Kabbalah, a form of Jewish mysticism that deals with how to decipher the Bible through numerology…I realized that the numerological meaning to ‘Ain’ was zero — it didn’t have a clearly defined meaning, and zero could mean everything as a whole, as a circle, or as something that has been accomplished, but at the same time it could also mean that something has been nullified — and I really liked that…It was exactly what I was looking for — something that I could put myself into and make into my own, rather than a name predefined by somebody else.”

Ain, who died suddenly of a heart attack on October 21, was much more than Celtic Frost’s bass player, as Fischer will readily admit. The two were creative partners in the deepest sense; in the Decibel interview, Fischer recalls meeting Ain at a party: “I sat down to talk to him, and he had all this occult knowledge, and I had all the historical knowledge, and we just bonded and spent nights talking about these topics. I would tell him what I had read, and he would tell me what he had read, and we just had endless material.” At times, Ain would supply source material for Fischer’s lyrics, like a book about Gilles de Rais that inspired the song “Into The Crypts Of Rays.”

As far as the actual sound of the group, Fischer brought a nightmarish, brain-scouring guitar tone and hellishly unhinged vocals, including his legendary “Unh!” Ain, though, bolstered that guitar sound with a low-end rumble that went far beyond “heavy” into some kind of subterranean pit of torment. He also designed the image — a seven-sided star from the writings of Aleister Crowley, pierced by five swords, with a screaming skull on top of it all — that adorned the group’s first EP, Morbid Tales.

Ain drifted in and out of the band; he wasn’t on their second album, 1985’s To Mega Therion, but he rejoined the lineup for a 1986 EP, Tragic Serenade, that included re-recordings of two TMT songs, “The Usurper” and “Jewel Throne.” When TMT was reissued in 1999, those songs were replaced with the versions from the EP. He returned for 1987’s wildly eclectic Into The Pandemonium (it included an EBM-influenced track, “One In Their Pride,” and a cover of Wall Of Voodoo’s “Mexican Radio”), writing or co-writing lyrics for three songs: “Mesmerized,” “Inner Sanctum,” and “Tristesses De La Lune,” which appeared in both a string-laden, French-language female vocal version and an English-language metal version as “Sorrows Of The Moon.”

Warrior disbanded the group after the tour for Pandemonium, and when he re-formed it a year later for Cold Lake, it was with all new musicians. Ain didn’t come back until 1990’s Vanity/Nemesis, an often overlooked album that blends thrash, Goth, and elements of industrial into a powerful and unique sound. Among his contributions were the lyrics to the hilariously named “Phallic Tantrum” and the twin title tracks. But the band split up again, and it would be another decade before Ain would make his ultimate statement within the context of Celtic Frost.

Monotheist, the band’s 2006 farewell album, was a true collaboration and labor of love between Tom Gabriel Fischer and Martin Eric Ain. They started working on it in 2000, and entered the studio for the first time in 2002. Ain contributed lyrics to seven and music to nine of the album’s tracks. He even delivered the incantatory lead vocals on the song “A Dying God Coming Into Human Flesh,” for which they shot an amazing video. Crawlingly slow and relentlessly heavy, Monotheist has a haunted, doomed feel that younger musicians just don’t have emotional access to. It’s an absolute masterpiece, and a monument to the decades-long creative relationship between Ain and Fischer. The group broke up for good in 2008, due to personal differences between the two men, but in 2016, Fischer wrote on his blog that “the loss of Celtic Frost, and thus the truly inimitable songwriting partnership with Martin Eric Ain, is something I will bemoan to some extent for the remainder of my days.”

Despite or maybe because they changed their sound radically on every album, Celtic Frost were massively influential on underground metal. Mayhem, Sepultura, Enslaved, and dozens of other bands have covered “Procreation (Of The Wicked)”; Marduk recorded “Into The Crypts Of Rays”; Dimmu Borgir covered “Nocturnal Fear”; High On Fire covered “The Usurper”; and multiple bands have used Celtic Frost album or song titles as names, including Therion and Nocturnal Fear. Morbid Tales laid out strategies hundreds of death metal and black metal acts would later ape, from the crunching guitars to the use of corpse paint, and To Mega Therion and Into The Pandemonium showed that there really were no rules. If you were confident enough in your own artistry, you could do anything you wanted. Like Ain said of his stage name, it was about refusing to be predefined by someone else. Even Monotheist was that kind of statement. First of all, nobody expected it at all, 16 years after the group’s last album, and for them to come back in such a world-flattening way was frankly astonishing. It might have ended acrimoniously, but for a year or two, it was glorious — a band absolutely peaking — and that was Ain’s triumph just as much as Fischer’s.