Mastodon will never be the next Metallica. The record industry has changed too much. Sales have slumped. Angry young white dudes with guitars aren’t what they used to be. Stars don’t look like Metallica’s tattooed giant James Hetfield or Mastodon’s scruffy Troy Sanders. Metal has changed, too, splintering into countless factions and fractions, all stretched between the underground and mainstream. Some of the form’s biggest defenders insist that the genre doesn’t need a popular messiah, that it’s satisfied with the fringes.

Still, the Georgia quartet has grown from a scrappy indie outfit into one of modern heavy metal’s great crossover success stories. When they headline Hopscotch’s main stage Saturday night, they’ll be one of the few young, loud acts that could pull it off. As critic Steven Hyden noted in a recent piece about pop-metal for Grantland, Mastodon’s career arc actually does reflect that of Metallica, perhaps more than that of any other modern metal group. Like Metallica, Mastodon’s first three albums earned them critical accolades from purists while shaping their profile outside the underground. And in both cases, their next albums sealed their mainstream fate: …And Justice for All raced up the charts, while Mastodon’s Crack the Skye almost cracked the Billboard Top 10, a feat that their actual breakthrough, 2011’s The Hunter, finally managed.

That album sold 75,000 copies in the United States. That’s a pittance compared to the 16 million units that Metallica’s fifth LP moved, but it’s staggering for most any band in 2014especially a metal band that’s relied on prog overtures, roared vocals and convoluted Thin Lizzy licks for so long.

And now they’ve released Once More ‘Round the Sun, their sixth album and their first with entirely clean vocals. The prog influences are diminished, and the sparkling pop-rock production adds a high-gloss finish. Once More ‘Round the Sun sounds like it could be their Black Albumthat is, the record that turned Metallica into superstars.

In arriving at Sun, though, they’ve jettisoned most of their more sludgy and abrasive trappings. They now lean hard on big rock hooks with saccharine vocal harmonies; their once concept-loaded lyrical approach has been simplified. Many of the Georgia heavies with which they emergedBaroness, Kylesa, Zoroasterfollowed a similar pattern, ditching rough-edged sludge for psychedelic or progressive touchstones. But does metal need to lose its edge to achieve mainstream success?

While Metallica sold millions before the Black Album dropped, its cleaner, ballad-heavy approach catapulted them into true stardom. If Once More ‘Round the Sun had featured the same roars and riffs as Mastodon’s cult debut, Remission, would it have cracked the Billboard Top 10? If Mastodon 2014 wasn’t dogged by Foo Fighters comparisons, would their shows greet the same clean-cut audiences? If Mastodon was still metal, would anyone but metalheads care about them?

Probably not: Prog aficionados, guitar geeks and metalheads cared about Mastodon at the start, but their real rise came only as they experimented with their sound and pursued new avenues. Their slow, steady ascent has never been as dramatic or meteoric as the shot to stardom that a young Metallica enjoyed, but they’ve relished the wiggle room. Mastodon’s star and sales figures have climbed only as they’ve expanded outside metal’s ironclad wallsinto adrenaline-fueled rock territory.

That might actually make Mastodon the new Metallica, but does it make them this era’s heavy metal heroes? That depends on where metal ends and rock ‘n’ roll begins, a question that both Metallica and Mastodon have only made more perplexing.

This article appeared in print with the headline “Metallishtodon”