There’s a particular moment in the new documentary “Searching for Sugar Man” that makes you realize you probably missed out on one of the great stories of American music.

In a sold-out stadium in South Africa, thousands of fans are stomping their feet and roaring as if the Rolling Stones are about to appear. Instead, they’re chanting the name of a singer-songwriter most people have never even heard of.

“Rodriguez!”

Suzanne Kreiter/Globe staff

“I didn’t have any choice about who he got to interview,” said musician Sixto Diaz Rodriguez (left) of director Malik Bendjelloul. “He pretty much had [the film] done by the time I met him in 2008.” Both were in Boston to promote Bendjelloul’s documentary “Searching for Sugar Man.”

That would be Sixto Diaz Rodriguez, who, on stage and off, goes simply by Rodriguez. “I’ve worked a long time for that name,” he says during an interview at a Boston hotel, where the film’s Swedish director, Malik Bendjelloul, was by his side.

The stadium concert marks the climax of “Searching for Sugar Man,” which unravels the extraordinary mystery of how a cult musician from Detroit became a huge star in South Africa — and never even knew about it until decades later. (For perspective on how vast the divide is, consider that Rodriguez will play Johnny D’s in Somerville — capacity 300 — in October.)

If you’ve never heard of Rodriguez, you’re among the masses. He recorded “Cold Fact,” his debut album, in 1969 and released it a year later on a small label that eventually went under. Its acoustic folk songs condemned political corruption and espoused a counterculture vibe that recalled early Bob Dylan. After making another record, 1971’s “Coming From Reality,” Rodriguez vanished from the public eye, living quietly as a father and laborer who worked various construction jobs to make ends meet.

Largely forgotten here, “Cold Fact” somehow made its way to South Africa, where it resonated with obsessive music collectors and young people who identified with its themes. In fact, the album’s anti-establishment overtone was right in line with the anti-apartheid movement and became a cornerstone of its soundtrack.

As in the United States, no one in South Africa knew anything about Rodriguez beyond the brief information printed on the back of “Cold Fact.” There were wild rumors that he had killed himself onstage, dispelled only when Stephen Segerman, a fan and record-store owner in South Africa, and music journalist Craig Bartholomew-Strydom set out to find Rodriguez. They were astonished to discover that he was alive.

Suzanne Kreiter/Globe staff

Swedish director Malik Bendjelloul.

From the film’s title to its narrative, “Searching for Sugar Man,” which opens Friday in the Boston area, plays up the suspense of his story. We don’t get a glimpse of Rodriguez in the flesh until halfway into the 90-minute feature. Even then, he comes across as reticent, uncomfortable with a camera trained on him for the first time in his life.

“Nothing beats reality,” he says in the film when asked if his life would have been better if he had known about his fame in South Africa. If he feels as though life dealt him a bum hand, he certainly doesn’t let on. “It’s the music business, so there’s no guarantees.”

Even with such a specific angle, director Bendjelloul cast a wide net to contrast Rodriguez’s modest stature in the United States with the incredible influence he had in South Africa. One newspaper headline crowed: “American zero, South African hero.” Asked in the film how many albums Rodriguez sold in this country, Clarence Avant, owner of Sussex Records, the defunct label that put out Rodriguez’s debut, says with only a trace of sarcasm: “In America? Six.”

Bendjelloul wasn’t aware of Rodriguez until a backpacking trip he took six years ago led him to Africa and South America, “looking for good stories.” He found one courtesy of Segerman, who was fascinated by Rodriguez’s music and the enigma around it. Bendjelloul knew what he had stumbled upon.

“It was a Cinderella story. It sounded like a fairytale, like it was scripted by a screenwriter,”

Hal Wilson/Sony Pictures Classics

Rodriguez, the mysterious 1970s rock 'n' roller, in "Searching for Sugar Man.”

Bendjelloul says. “I knew someone had to make this movie.”

Bendjelloul, 34, lives in Stockholm and had previously worked for Swedish television, making documentaries on artists such as Björk and Kraft-werk. Four years in the making, “Searching for Sugar Man” is his feature filmmaking debut.

He hadn’t made contact with Rodriguez at the time he was considering the movie. In fact, he wasn’t even sure if Rodriguez would be part of it. Rodriguez, it turned out, wasn’t exactly ready for his close-up.

“I was skeptical, resistant, reluctant. I didn’t have any choice about who he got to interview. He did all of that himself,” Rodriguez says. “He pretty much had it done by the time I met him in 2008.”

“Rodriguez said, ‘I’m not a film star, Malik, I’m a musician,’” Bendjelloul remembers. “But I felt like this is a big story, and everyone involved thought so, too. And for me this film proved I was right.”

Malik Bendjelloul/Sony Pictures Classics

Rodriguez in a scene from "Searching for Sugar Man.”

In person, Rodriguez is more forthcoming than he appears to be in the documentary. He’s 70, and if the body is a little feeble, his mind is astute. The film’s publicity campaign has put him back on the road, for both screenings and concerts.

There’s even some buzz surrounding him. His performance at last weekend’s Newport Folk Festival, on an intimate stage in a museum, was so packed that curious spectators crowded together and peered in through the open windows. Dressed head to toe in black, with his eyes concealed behind dark sunglasses, Rodriguez looked like a renegade who hasn’t changed his clothes — or his deeply held convictions — since the late ’60s.

The film, which takes its name from Rodriguez’s song “Sugar Man,” makes the case that he was woefully overlooked. (Culling from both of Rodriguez’s ’70s albums, the movie’s soundtrack is a good introduction to his craft.)

“This guy deserves recognition. Nobody in America had even heard of him,” Steve Rowland, who produced Rodriguez’s second album, says in one of the movie’s interviews. “Nobody was even interested in listening to him. How can that be, a guy that writes like this?”

Rodriguez did, however, have an adoring fan base. It just happened to be in a country he had never stepped foot in. As documented in “Searching for Sugar Man,” on his first trip to South Africa in 1998, once Rodriguez had learned of his popularity, he traveled there with his three daughters in tow. Limousines and well-wishers greeted them at the airport; his daughter Regan recalled thinking that the limos were for someone else, “someone important.”

According to the film’s closing credits, Rodriguez has returned to South Africa four times, playing 30 concerts and giving away most of the money he’s made on those tours. He still lives in downtown Detroit, in the same house he’s called home for 40 years.

With a documentary about him now making its way to theaters and a tour taking him across the country, Rodriguez says he’s been humbled by all the attention. After all, it eluded him for 40 years.

“This film is going to play in 120 cities,” Rodriguez says. “If I had been played on 84 jukeboxes, I would have been thrilled.”