#Frank Zappa, unlikely rock star, subject of new documentary by Alex Winter

With his eccentric, experimental music, the rock iconoclast believed that, for all of his influential innovation, he was seen as a “threat” in the industry.

“Basically, my career has been, year after year, waiting to be disposed of,” says the late legend in the new documentary “Zappa,” which arrives on demand Friday.

But, before dying of prostate cancer at 52 in 1993, Zappa would build a Rock & Rock Hall of Fame résumé over 62 albums released in his lifetime. His game-changing legacy is explored through interviews, archival footage and intimate access in “Zappa,” which is directed by Alex Winter (Bill of the “Bill & Ted” movies).

The film opens with Zappa taking the stage for his last recorded guitar performances in 1991 at a celebration of the withdrawal of Russian troops in Prague, Czech Republic. “This is just the beginning of your new future in this country,” he says, even as he knew his own life was ending.

Later, “Zappa” reveals that, in an unlikely career twist for a rock star, he became the Czech cultural and trade representative to the US in his final years.

After taking you inside the personal vault of his life’s work that Zappa kept at his home in the Laurel Canyon neighborhood of Los Angeles, the film goes back to his beginnings as a Baltimore kid who — with a father who worked at the poisonous gas manufacturer Edgewood Arsenal — was more into chemistry growing up.

Then, after his family moved to California, he went from playing with gas masks to playing guitar. “When I first picked up the guitar, I said, ‘How in the world can anybody get any sound outta this thing?’ ” he says, adding that blues axmen such as Guitar Slim and Johnny “Guitar” Watson showed him the way.

As a struggling musician, Zappa worked as a commercial artist with his own greeting-card line before getting his own studio and forming his band, the Mothers of Invention, so that he could play all the music he was writing.

An obsessive perfectionist, he had exacting standards for his bandmates — who he once called “trained monkeys,” according to one of the musicians interviewed — but the “music theater” that they made was groundbreaking right down to the album-cover art.

In fact, the group’s debut LP, 1966’s “Freak Out!,” would even influence The Beatles’ classic “Sgt. Pepper’s Lonely Hearts Club Band” in 1967.

“A lot of what we do is designed to annoy people to the point where they might just burst up and question enough of their environment to do something about it,” Zappa says of the Mothers of Invention.

But “Zappa” reveals that in one surprising way, he went against the counterculture flow in the ’60s: He was anti-drug.

Still, he famously fought against the censorship of the Parents Music Resource Center (PMRC) in the ’80s. And he fought for his own artist rights, becoming an astute businessman with his own label.

The film also goes inside Zappa’s personal life, including interviews with his wife and business partner Gail Zappa, who he met while she was working at the famous Whisky a Go Go in Los Angeles. (Gail died in 2015, and the documentary is dedicated to her.)

Zappa wasn’t always around for his family, missing the birth of his first child, daughter Moon Unit, in 1967. “I said, ‘Well, if it’s a girl, name [her] Moon, and if it’s a boy, name him Motorhead,’ ” he says.

Teaming up with the oldest of his four children, Zappa would score his first-and-only Top 40 hit, “Valley Girl,” in 1982. But the mainstream was never the place for Zappa, whose avant-garde music fused everything from jazz to classical.

“I really think Frank is afraid to have a hit record, because I think Frank could’ve written hit records all day,” says Alice Cooper, who was signed by Zappa at the beginning of his career. “And he purposely sabotaged a lot of his records. It was interesting ’cause everybody was going for the hit record — and he never did.”