In 1995, on the cusp of metal’s darkest, nü-est era, Pantera was arguably the biggest heavy band in the world. The Texas-based foursome was coming off a three-album run of platinum records — 1990’s Cowboys From Hell, 1992’s Vulgar Display Of Power, and 1994’s Far Beyond Driven. After spending the ’80s offering up a hard-edged take on glam metal, they added the Louisiana native Phil Anselmo to the lineup, a vocal chameleon who could reach for the sky like Rob Halford (the climax of “Cemetery Gates”) or spit venom like he was in an NYHC band (“Fucking Hostile”). Almost overnight, Pantera became a new kind of band, a novel-at-the-time amalgam of hardcore and thrash that would come to be known as groove metal. (Anselmo did sing on one of Pantera’s glam records, 1988’s Power Metal, but even that takes on a thrashier bent thanks to his presence.)

Pantera’s ascension made the band’s members, especially Anselmo and guitarist “Dimebag” Darrell Abbott, into blue-collar rock stars. They cut an image — one unfortunately associated with the imagery of the Confederate South, it has to be mentioned — that no metal band had quite managed to pull off before, and vast swaths of fans who felt cut off from the genre’s traditional mainstream centers in England and California finally had megastars they could call their own. By 1995, a restless Anselmo had begun to figure out how to use his position as a Southern metal god to become an evangelist for the underground metal he loved. His first major coup in that role was the formation of Down, whose brilliant debut, NOLA, turns 20 tomorrow.

Down united Anselmo with Eyehategod’s Jimmy Bower, Crowbar’s Kirk Windstein, and Corrosion Of Conformity’s Pepper Keenan, and suddenly tens of thousands of Pantera fans were familiar with three essential bands of the Southern metal underground. Eyehategod, Crowbar, and CoC had put out a half dozen great records between them by the time NOLA dropped, but beyond their Louisiana backyard, they hadn’t found significant commercial success. With the dude who sang “Walk” behind the mic, they had a top 40 hit and spent six weeks on the Billboard albums chart. For casual metalheads, the Deep South was finally on the map.

Of course, if the songsweren’t any good, Anselmo’s presence alone wouldn’t have made NOLA a hit. Its 13 tracks are a deep well of mean, twangy riffs from Keenan and Windstein, surprisingly nimble drumming by Bower, who played guitar in Eyehategod, and unstoppable vocal hooks from Anselmo, who’s clearly having the time of his life. Despite the band’s obvious Southern bona fides, a pronounced grunge influence looms large on the songwriting. The result is a shockingly effective midpoint between Soundgarden and Skynyrd — the sound of a Pike Place monger throwing a fish directly into a Bourbon Street po’ boy shop. “Stone The Crow,” that lone top 40 hit, is the purest distillation of that sound. Anselmo channels Chris Cornell (and, for a moment, Tool’s Maynard James Keenan) over harmonized riffing from Keenan and Windstein. A huge chorus delivers the song to pay dirt, but it doesn’t really get aggressive until the very end of the song. Instead, the whole band leans into the strength of the melodies and the relatively gentle — if a bit dour — vibe of the song, thus exorcising the expectations wrought by their primary projects.

On the whole, NOLA turns out to be significantly less heavy than the sum of its parts, and that’s what makes it so effective. Everyone involved sounds liberated. In Eyehategod, the ravages of substance abuse haunt every depraved passage. In Down, we get a bong-rip instrumental break in a song called “Hail the Leaf.” (Heroin took its toll on Anselmo as well, but that’s left mostly abstract here when it comes up at all.) Whereas Kirk Windstein’s playing in Crowbar tends to pursue an end-of-the-world heaviness akin to early Black Sabbath, and Pepper Keenan helped transform Corrosion Of Conformity from a crossover band into the blueprint for Southern sludge, Down sees them throwing down some serious party riffs. Harmonized leads abound, and some passages feel so loosely improvised that it’s easy to imagine these two guys just kicking some licks around in some smoky, empty bar Baton Rouge bar.

Anselmo sounds freest of all. There’s very little of the tough-guy/motivational-speaker bluster that defined his role as Pantera’s frontman. His considerable vocal range stretches all over these songs, and even the ones that could have ended up being a bit pedestrian are put over the top by his performances. If Down was a project meant to help lift all boats in Southern metal, it couldn’t have asked for a better mouthpiece.

But the mainstreaming of fellow Southern metal luminaries wasn’t Anselmo’s only act of patronage for the genre. Around the same time Down was getting started, he started talking up black metal bands in magazine interviews, most notably and frequently Darkthrone. He put out two demos with the sorta-jokey Christ Inversion — another New Orleans supergroup, but this time with corpsepaint. That led to the more serious black metal project Viking Crown, with his then-wife Opal Enthroned on keyboards and death metal legend Killjoy of Necrophagia on vocals. Throughout this era, Anselmo remained a highly visible figure in metal’s mainstream as the singer of Pantera and Down. It’s not unreasonable to suggest that black metal ultimately became a force in America at least partly because of his backing.

After Pantera’s dissolution in 2003 and Dimebag’s horrifying onstage murder in 2004, Anselmo became even more devoted to promulgating extreme metal. The founding of Housecore Records in 2008 and the Housecore Horror Festival in 2013 represented a huge financial commitment to his favorite cause. He’s like a much wealthier version of his erstwhile idol and current pal Fenriz, even often riding for the same bands; Portal and Ghost leap to mind immediately, and their respective profile bumps probably have plenty do with their famous fan’s tireless advocacy.

NOLA may have kickstarted Phil Anselmo’s second career as an ambassador for metal’s underground forms, but it resonates today for many more reasons than that. We’ve been over the songs already, but they really do beg deeper investigation into the catalogs of the members. Corrosion of Conformity, Crowbar, and Eyehategod have all put out great work recently, and Down — now with an ex-member of Goatwhore in tow — has released two more full-lengths and two EPs in the years since NOLA. The membership of Down marks the origin point for a map of Southern metal, one with as many endless overlapping points and permutations as those of the famous scenes in the Bay Area or Gothenburg. Our modern understanding of what metal in the Deep South sounds like and means starts with NOLA, and we should pay our respects.