If the histories of Jimmy Iovine and Dr. Dre warrant four hours of prime HBO real estate in “The Defiant Ones,” then certainly Michael Alago, the flamboyant New York punk habitue who signed Metallica to Elektra and White Zombie to Geffen during his stints as an A&R executive, deserves his 77 minutes of recognition.

In the spirit of similar documentaries on behind-the-scenes heroes such as Rodney Bingenheimer (“The Mayor of Sunset Strip”) and Danny Fields (“Danny Says”), “Who the F**k Is That Guy?” recounts the remarkable journey of Alago, a Puerto Rican kid who grew up on Brooklyn’s New Utrecht Avenue with his bedroom facing an elevated subway track. That undoubtedly influenced his passion for post-punk hardcore rock. “I love the noise,” he says at one point in the movie. “I love the sweat.  I love when I go to concerts and it’s 99% guys.”

The documentary was directed by punk-rock veteran Drew Stone, who previously helmed a 2012 doc on Boston hardcore, “All Ages: The Boston Hardcore Film,” and was inspired by constantly running into Alago and asking himself the movie’s title question. Distributed by LA. indie XLrator, the film opens in select theaters on Friday (July 21) before hitting VOD and iTunes the following Tuesday (July 25).

New York native Stone raised $30,000 through a Kickstarter campaign, got a matching advance from XLrator, and received post-production contributions from Rob Zombie and “Please Kill Me” author Gillian McKay (as executive producers), along with Cyndi Lauper and veteran New York rocker Jesse Malin (as producers).

“Michael is so loved, that people just wanted to give back,” says Stone, who still performs with his group Antidote, which emerged from the early-‘80s Lower East Side hardcore scene that produced Cro-Mags, the Misfits, Agnostic Front and Sick Of It All, all of them Alago faves.

Michael Alago’s career trajectory could only have taken place in the ‘70s, where he began hanging out as an underage teen on the CBGB/Max’s Kansas City circuit, publishing a xeroxed fanzine dedicated to the Dead Boys, before getting hired off the street at 19 by Jerry Brandt as his assistant at the just-opened the East 11th Street nightclub The Ritz (now Webster Hall). He eventually became the club’s booker, where he hired Public Image Ltd. for an infamous 1981 riot where the band played behind a curtain with projected images and refused to come out, as beer bottles rained down on the stage and a riot spilled onto the streets quelled by police on horseback. That began Alago’s three-decade-plus friendship with a pugnacious John Lydon, one of the film’s talking heads, who offers the following endorsement, “He stands really rigidly in my very small collection of very important people that don’t lie.”

Brandt recommended Alago to Elektra head Bob Krasnow, and the ambitious 22-year-old immediately made his mark by signing Metallica to their first major-label deal after hearing a homemade cassette (which he shows on screen) and seeing them at a Roseland Ballroom show.  From there, he landed in the New York office of Geffen Records, where he brought in a young indie-metal band named White Zombie, which emerged out of the same post-punk hardcore scene as director Stone’s band Antidote.

The openly gay Alago represented a breath of fresh air on the sometimes casually homophobic world of metal.  “My sexuality was never a problem with any artist I ever worked with,” he explains. “When somebody is honest, truthful and an open book, that helps.  I was always myself.  And that breaks down so many barriers. There’s no need to talk about sexuality, when all we really want to talk about is music.”

It was Alago’s love for all kinds of music that initially attracted Stone to the project, and indeed his eclectic tastes run the gamut from the most aggro metal to working with a young Tracy Chapman on her debut, overseeing longtime idol Nina Simone’s final studio album in 1993, “A Single Woman,” while at Elektra, and independently A&R’ing two Cyndi Lauper records in 2009 and 2010.

The film’s interview subjects reflect Alago’s wide-ranging aesthetic, and represent glowing testimonials from Metallica’s James Hetfield, Lars Ulrich, Kirk Hammett and Jason Newsted, Rob Zombie, Cyndi Lauper, Cherry Vanilla, Metal Church guitarist Kurdt Vanderhoof (who admits ultimately bonding with him over being gay), Eric Bogosian and Lydon.

“It was heartwarming and incredible that all these artists said yes when we asked them to be in the movie,” says Alago.

The movie doesn’t flinch from its subject’s demons, either, recounting Alago’s descent into addiction and his narrow brush with death after being diagnosed HIV positive, but unlike many an episode of “Behind The Music,” this one has a happy ending.

Now clean and sober since stepping away from the music business in 2004 after 25 years, Alago has set out to follow his own artistic passions, publishing a poetry book (“Night Blooming Jasmine Will Never Smell The Same” with Life of Agony’s transgender singer Mina Caputo) and a series of “Rough Gods” photography collections put out by notorious Berlin publisher Bruno Gmunder (who earlier this year declared bankruptcy), where his Robert Mapplethorpe-inspired work involves “taking pictures of big, strong, muscular, tattooed and sometimes scarred men. Because that’s what I like to look at.”

Stone has come to appreciate that Puerto Rican kid he used to see everywhere and wonder who he was. “I didn’t know the depth of his story when I started,” he says, “But he changed the face of the music business as we know it.”

Alago’s just happy to have survived. “In many way, it’s a cautionary tale of how the music business can get to you and almost kill you,” he declares. “But as I tell everyone, I’m so happy that this documentary is about me being alive, flourishing and doing well. It’s all a blessing.”

Ramones producer/guitarist Daniel Rey has the last word in the film. “I remember seeing him at the front of the line one night at CBGBs to see Patti Smith, thinking ‘He must be a real rock ‘n’ roll fan.”

According to “Who the F**k Is That Guy?,” Michael Alago is that and a whole lot more.