ONCE, TWICE, THREE TIMES A HADES Franco Sesa, Tom Gabriel Fischer and Martin Eric Ain, left to right, get cross with each other.

“When I was young, I thought that at my age, life would be over. Now I realize that the real heaviness, the real darkness, is now inside of me like it has never been.”

Tom Gabriel Fischer’s eyes are still kohl-rimmed, but they are sunken with age, the lines on his face harsher than before. “Things have to be different now,” he explains. “It’s not the ’80s anymore. If you haven’t changed since then, there’s something wrong with you.”

His look may have spawned a generation of corpse-painted European metal bands, but as the founder of Switzerland’s Celtic Frost, Fischer’s real legacy was laying the groundwork for what would become some of the bleakest forms of black metal. By wielding classical music and electronics as fiercely as his trademark serrated guitar tone, he was also one of the first to bring metal into the avant-garde, a vision that culminated on 1987’s landmark album Into the Pandemonium. That vision soon blurred after a failed 1988 commercial stab at glam, and grew even dimmer when Fischer’s strained relationship with founding bassist Martin Eric Ain led to an apparently permanent split in 1991. The band’s legacy seemed relegated to a mere footnote in metal’s history.

But Celtic Frost’s story wasn’t over yet. A decade later, when asked by their former record company to remaster their back catalog, Fischer and Ain began discussing the possibility of recording again. “For the first time, Tom and me really had to get together and talk about the past,” Ain says. “All of us were wrestling with personal demons, and this was all coming out in the music.” After four years of exorcising and recording three albums’ worth of material, the pair produced Monotheist, a masterstroke that’s one of the best extreme metal albums of 2006.

While British band Venom coined a music genre with its 1982 album Black Metal, its gleefully ghoulish thrash and pentagram dangling seemed cartoonish compared to Celtic Frost’s grave treatment of the occult. But Fischer makes it clear that they’re not, and have never been, disciples of the devil. “Occult doesn’t mean you’re satanic, or Christian,” he says. “It just means you’re dealing with the topic of occultism. None of us practice any religion. But we follow history and current events, and how can you not be interested in what drives mankind?”

“We certainly weren’t the first band to deal with the occult,” Ain adds. “That would be the originators of everything heavy: Black Sabbath. But maybe we took it more seriously. I try to do it from more of an agnostic point of view. I don’t consider myself a religious person. I have my beliefs, and I leave faith to every human being, because faith is a part of life. I can’t help but think, though, that organized religion is, in a fundamental way, completely wrong.”

Still, it can’t be denied that European black metal’s bloody second wave took such heathen cues and went spiraling down into hell with them, leading to several headline-grabbing satanic-related incidents and murders. “I, and I believe Martin as well, had a hard time associating with the elements of the black-metal scene during a certain time of the 1990s,” Fischer says. “Certain things that were done went far beyond what music was supposed to create. It made it very difficult to look back on our own history with black metal. Nowadays, I believe, the black-metal scene has come of age, and is developing into something very interesting. It is not as one-dimensional as it once was.”

Those black-metal fans will be out in legion this week when, joined by Swiss drummer Franco Sesa, Celtic Frost plays Chicago for the first time in years. “Chicago was the first show we played in the U.S. ever,” Ain recalls of the band’s 1985 To Mega Therion tour stop. Despite a series of mishaps—including losing all its gear—the band played what Ain considers one of the best concerts of its career. “I was 17 and completely overwhelmed. Here I am in the U.S. for the first time, and people are going completely ballistic. It was one of the most lasting life experiences I’ve ever had.” And this time around? “I hope they’ll all be back. Although,” he says with a chuckle, “they probably won’t jump around the way they used to.”

Celtic Frost plays Vic Theatre Saturday 23.