It's no overstatement to say the Melvins thoroughly reformulated the sound of heavy guitar music in America in both the punk underground and the hard-rock mainstream. This is no small feat, considering that the band—cofounded by guitarist Buzz Osborne and drummer Dale Crover in Montesano, Washington, in 1983—have always been unconventional cult artists. Across their first five full-lengths, from 1987’s Gluey Porch Treatments to 1993’s Houdini, they developed a grinding synthesis of Black Sabbath-inspired metal and hardcore punk aggression that influenced not only Nirvana and grunge but also sludge, stoner rock, doom and drone metal. The Melvins aren’t just heavy, however: they’re weird and irreverent, too. You can hear it in Osborne’s gnarled bellows and absurdist lyrics. That sensibility also explains why their records—especially those released after hooking up with Mike Patton’s Ipecac label in 1999—boast such wildly different personalities. Their 2004 collaboration with industrial pioneer Lustmord descends into dark ambient; by contrast, 2018’s Pinkus Abortion Technician is a slab of ’70s rock worship featuring Butthole Surfers legend Jeff Pinkus on bass. There’s real freedom in the Melvins’ unpredictability, and it’s just as central to their legacy as all their brilliantly crawling riffs and thunderous grooves.