No one was more surprised than Michael Bishop when Joan Rivers told him how much she loved his band. It was 1990, and Bishop and Dave Brockie, his bandmate in US shock-metal provocateurs Gwar, were guests on Rivers’ TV talkshow. The pair were in full intergalactic barbarian-warrior regalia, complete with grotesque latex monster mask (Brockie) and full-face gladiator helmet topped off with a gigantic spiked mohawk (Bishop).

“When they cut to a commercial, she said, ‘This is so great, you guys are so creative. When I was a kid I would have loved this’,” recalls Bishop, who joined the band as bassist in 1987, adopting the stage name Beefcake the Mighty. “I was, like, really? Wow!”

Perhaps her admiration shouldn’t have been so unexpected. Like Rivers before them, Gwar were champion button-pushers who thrived on trolling the uptight. A fascinating new documentary, This Is Gwar, charts their almost 40-year history, presenting a band whose wilfully crude aesthetic masks both a satirical edge and an artistic spirit. As former member Danielle Stampe – AKA dancer, vocalist and self-proclaimed “mother goddess” Slymenstra Hymen – puts it today: “Gwar was this punk-rock opera put together by a bunch of crazy artists and musicians.”

That description fits Hunter Jackson and Brockie, the two mavericks who breathed life into Gwar in the mid-80s. Jackson was an artist, sculptor and film-maker; Brockie was the frontman of local punk-rock band Death Piggy. They shared a sense of humour and DIY ethic. Bishop remembers: “Hunter was a super-creative guy and Brockie had a very big personality – he was allergic to sincerity. There was a tension between them from the start, but it was a productive tension.”

The Gwar mythos was in place early on courtesy of Jackson: broadly, a bunch of misfit alien warriors banished to Earth millennia ago. Singer and guitarist Brockie became Oderus Urungus, and head artist and sometime co-vocalist Jackson christened himself Techno Destructo. Stampe’s own choice of persona reflected her interest in Greek mythology.

“I wanted Slymenstra Hymen to be this feminist icon that guys would be in love with and be terrified of at the same time,” says Stampe, whose dominatrix-esque presence was accessorised with male “slaves” on chains.

They leaned into their love of shlock early on. Like an X-rated version of Kiss or Alice Cooper, they showered audiences with fake blood and semen ejaculated from severed heads and arms or, in the case of Brockie, an oversized prosthetic penis nicknamed the Cuttlefish of Cthulhu. “It was performance art, in that the band was looking for a way to break down that wall between the audience and the performance,” says Bishop.

The band’s costumes and stage props were created by a team of sculptors and artists in the Slave Pit, a twisted, B-movie version of Andy Warhol’s Factory housed in a disused milk-bottling plant in their hometown of Richmond, Virginia. As a result, gigs and tours were labour-intensive and expensive. “Gwar always lost money on the shows, and that has never stopped,” says Bishop.

What gigs lacked in financial reward, they made up for in a sense of shared, if sticky, communion. “It was like this bacchanalian rite of passage,” says Stampe of the Gwar live experience. “It was a place where geeky kids who were into fringe stuff could let loose, dress up and be themselves.”

One of those geeks was Dave Grohl, who turned down the chance to join the band in the late 80s. Another was comic Weird Al Yankovic. “I don’t know why people think having a sense of humour does not go along with rocking,” says Yankovic in This Is Gwar. “It doesn’t work if you don’t have the skill and talent to back it up, and Gwar have the talent.”

Not everyone shared that view. In 1990, a show in Charlotte, North Carolina, was halted by the local police department, who objected to the sight of a “priest” being sexually assaulted with a crucifix. When the cops failed to find the priest backstage, they arrested Brockie instead, charging him with obscenity.

“They made him take off his costume except for the big dick,” says Bishop. “They took a bunch of pictures, then put the dick in a five-gallon bucket and took it away.” The seriousness of the subsequent court case was undercut by the fact that the judge’s name was Dick Boner. “It was just so profoundly absurd,” says Bishop. Brockie received a suspended sentence, and Gwar were banned from playing North Carolina for a year.

While Gwar’s notoriety dimmed as the 90s progressed, their occasional intersections with mainstream culture continued. They popped up in the 1995 Liv Tyler movie Empire Records, and appeared on an episode of The Jerry Springer Show, where they were confronted by the irate mother of a 14-year-old fan named Shaun. Springer himself seemed to be in on the joke, even joining the band on stage at one of their shows – an appearance that concluded with him being eaten by a giant anus.

If oversized penises and giant anuses sound puerile, that’s because they are. But they were also a blunt rejoinder to the snobbishness and self-importance of the art world. As Bishop puts it: “Gwar was a group of people who went to art school and had a reaction against it, because the things they liked were belittled and dismissed.”

It turned out a lot of people still feel the same way. Gwar have accumulated an ardent following down the years, with fans – nicknamed bohabs – often turning up to shows in homemade outfits.

“What I love about Gwar is that they’re a living comic book,” says Lani Hernandez-David, a 20-year-old bohab from London. He had been creating latex masks of comic-book characters since his early teens, but discovering Gwar gave him a whole new inspiration. “I watched hours of footage,” he says. “With Covid, it was an escape from the harsh reality of not being able to go outdoors for so long.”

Despite the band’s best efforts, reality has inevitably intruded into the comic-book world they created. In 2011, guitarist Cory Smoot was found dead on the band’s tour bus, the result of a pre-existing heart condition. Five years ago, longtime guitarist Mike Derks, AKA Balsac the Jaws of Death, was diagnosed with a rare form of blood cancer, though he has since recovered.

But the biggest blow came in 2014, when Gwar co-founder Brockie died of a heroin overdose. “He was a genius,” says Stampe, her voice breaking with emotion. “He could be a real asshole, but he was a wonderful leader. I miss him every day.”

Brockie’s death was marked by tributes from many of his contemporaries, as well as The Daily Show host Jon Stewart, who had seen Gwar play when he worked as a bartender in a New Jersey club in the late 80s. The band held a public memorial at that year’s Gwar B-Q, the festival-cum-fan-convention thrown annually since 2009 in Richmond, Virginia. Brockie’s Oderus Urungus costume was laid out on a Viking-style bier, floating on a nearby lake. An archer fired a flaming arrow at the boat, at which point the fibre-glass raft combusted.

“There were these 30ft-high flames and jet-black smoke,” says Bishop. “All of a sudden, it starts careening over towards the people who are watching on the shore. It was just chaos, which was kind of fitting.”

That Gwar elected to continue without their talismanic leader is no surprise given the turnover of members they’ve had – upwards of 40 people have passed through the band. Minus some brief reappearances since, Jackson and Stampe left in 2000 (Stampe subsequently embarked on a successful career as a set designer, working with the likes of Katy Perry and Lady Gaga). Bishop left Gwar in 1993, before briefly coming back at the end of the decade. After Brockie’s death, he returned for his third stint, this time as a new character, Blöthar the Berserker.

There may be no original members of Gwar left but their blend of puerility and subversion remains intact. Their latest album, the metallic The New Dark Ages, is a characteristically sly commentary on a post-Trump world. “There’s almost been this return to barbarism,” says Bishop. “Everybody is at odds with each other. That guy just obliterated the idea of truth.”

And Gwar themselves? Their barbarism has never gone away; nor has the commitment it takes to bring it to life. “I sometimes wonder why more bands haven’t done things the way we’ve done them,” says Bishop. “Then I realise they don’t have to dress up as ridiculous rubber monsters and play the way we play every night. Being in Gwar is fucking hard.”

• This Is Gwar is available on Shudder from 21 July. The New Dark Ages is out now on Pit Records.

• This article was amended on 17 July 2022 to refer to “severed heads” rather than “decapitated heads”; something that is decapitated has had its head removed.