With its cult of charisma, sex appeal, and genius, it’s natural that pop music should favor a “great man” view of history. To this way of thinking, rock ‘n’ roll was birthed by Elvis, punk by Johnny Rotten, and grunge with Kurt Cobain. The reality is messier and more interesting: Behind each of these watershed artists lies a dense web of influences and innovators that helped to set the stage for their breakthroughs. It’s still a “great man” theory, there are just many more of them.

Of those that contributed to Nirvana’s breakthrough, none looms larger than Dinosaur Jr., which, more so than any other late 1980s underground band, anticipated the sound and ethos of grunge. The reissue this week of Dinosaur Jr.’s first three albums – “Dinosaur,” “You’re Living All Over Me,” and “Bug” – on Merge Records offers occasion to reconsider this un(der)sung band, and to revisit the period just before punk broke into the mainstream.

With the advantage of hindsight, Dinosaur Jr.’s J. Mascis looks like some kind of Gen X reject archetype. He was born into the comfortable middle-class community of Amherst, Mass., which, with its listless VW deadhead tradition, is every bit as logical a birthplace for slacker culture as Seattle. But at a time when the underground was full of straight-edge hardcore kids with shorn heads and ascetic ways, Mascis was sloppy and directionless. He wore his hair long, often in a big rats’ nest like his hero Nick Cave, and dressed in grubby flannel – more or less anticipating, if not dictating, the whole grunge aesthetic.

Musically, Dinosaur Jr.’s sound was as much a circling back as a step forward. In the 1970s, punk had defined itself against the musical excess of stadium rock; it boiled rock ‘n’ roll down to bare bones, and hardcore whittled it further: to a couple chords, a couple minutes, a few barked words. Then comes Mascis, out of nowhere, like some doofus guitar-rock messiah, playing hardcore songs with big Neil Young solos plunked right in the middle. He was among the first to find inspiration, equally, in the music of Black Flag and Black Sabbath.

On “Dinosaur,” the band’s 1985 self-titled debut (the Jr. would be appended later to distinguish them from another band), you can hear Mascis circling the sound that would define grunge, almost summoning it. All the essential elements are here: the heavy bass and sludgy guitars, the self-loathing, the throaty howl. Songs like “The Leper,” “Pointless,” and “Repulsion” wouldn’t have been out of place on Nirvana’s “Bleach,” which would come out four years later.

But of the three albums reissued by Merge, the most essential is “You’re Living All Over Me,” originally issued by SST in 1987. Sub Pop gets all the credit for midwifing grunge, but SST was, by that time, home to an impressive proto-grunge stable, including the Screaming Trees, Soundgarden, the Meat Puppets, and Sonic Youth. Mascis called his sound “ear-bleeding country,” and it’s easy to see why: The songs have catchy melodies and are sung in a faux-county drawl, but they’re blown apart by searing wah-wah guitar solos and blasts of white noise. This is the album that made it cool for indie rockers to aspire to be guitar gods again.

As with so many other American underground innovations, the British were the first to recognize Dinosaur Jr.’s genius. The British music press adored Mascis’s seemingly dumb, raw, authentic, inarticulate, American anomie. They asked him clever questions and read inexpressible depth into his single-syllable replies. In many ways, the band’s 1987 European tour was a trial run – in tone and style – for the hyperbolic coverage that would put Seattle and grunge on the map a few years later.

But to view Dinosaur Jr. only as a proto-grunge band does it a disservice. Just as a Ramones tour sowed the seeds of punk in the U.K., Dinosaur Jr.’s U.K. tour set the stage for the cascading guitars of British shoegazer bands like Ride and My Bloody Valentine. Mascis also stuck around in America when grunge broke. After dumping his band mates and signing to a major label, he churned out early alt-rock classics such “the Wagon,” “Start Choppin,” and “Feel the Pain,” though he never quite recaptured the energy or realized the promise of his early work.

And then there’s Sebadoh, Lou Barlow’s side project, which would become one of the quintessential lo-fi bands of the 1990s. As the bassist for Dinosaur Jr., Barlow was forever in Mascis’s shadow and under his thumb. His home recordings became an outlet for his musical ideas and a vent for his rage (both are previewed on the early “You’re Living All Over Me” track “Poledo,” which alternates between acoustic strumming and warped tape experiments).

As chronicled in Michael Azzerad’s “Our Band Could Be Your Life,” the relationship between them sounds impossibly dysfunctional. But it seems time and opportunity heal all wounds: prompted by the reissue of the albums, the original Dinosaur Jr. lineup (Mascis, Barlow, and Murph) is reuniting to play festivals this summer.