Before there was Ovitz or Ari, there was Sue Mengers.

During the peak of her clout in the 1970s, the brash barrier-breaker helped popularize the idea of the Hollywood super-agent. The media lapped up her comic crudity (after the Manson family murdered actress Sharon Tate, she told a frightened Barbra Streisand, “Don’t worry, honey, they’re not killing stars, only featured players”), her legendary dinner parties attracted Tinseltown’s A-list, and “60 Minutes” came calling to do a lengthy interview that captured Mengers dishing and deal-making.

She was so larger than life that she inspired both fictional knockoffs, such as the fast-talking agent portrayed by Dyan Cannon in “The Last of Sheila” and hit Broadway plays like “I’ll Eat You Last,” which had Bette Midler offering a wicked send-up of the legendary tenpercenter. Yet biographer Brian Kellow, fresh off his acclaimed book “Pauline Kael: A Life in the Dark,” was trepidatious about tackling Mengers.

“I’m pretty picky about my subject matter,” Kellow said.

Ultimately, after much pressure from his agent, Kellow came around, partly because he could envision Mengers’ rise from an impoverished childhood in the Bronx to the best table at Ma Maison as “a comic biography.” The fruits of his labor and his 200-plus interviews with Mengers’ clients and intimates like Candice Bergen, Ryan O’Neal, Ali MacGraw, Barry Diller, Robert Evans and, her crown jewel, Barbra Streisand, is entitled “Can I Go Now?” It hits stores next Tuesday, Sept. 8.

“She had a wild personality,” Kellow said. “She would say anything to the most famous and celebrated people and she got away with it. That kind of brutal honesty never goes out of fashion.”

Mengers, Kellow notes, was so disarming that she completely charmed Israeli President Shimon Peres during an intimate sit-down with him by spilling secrets about which stars were bed-hopping.

She didn’t believe in gussying up hard truths and could be brutally candid with her clients. That lost her some accounts (prickly Faye Dunaway didn’t stay long; Streisand left in part because Mengers hated the idea for “Yentl”), but it also earned her respect.

“Everyone prized her honesty,” Kellow said. “In a town like Hollywood, that’s hard to come by. Instead of yes-yesing or kissing up, she would say, ‘You’re too fat’ or ‘Your hair looks terrible,’ but it was all in service of getting them work. She was a scrutinizing, tough Jewish mama.”

Oddly enough, though Mengers was one of the first women to climb the agency ladder and wielded power in an industry that was very much a man’s club, she didn’t see herself as a feminist. In fact, she had very traditional ideas of gender roles, constantly advising her female clients to find rich husbands.

“I don’t think she had the time of day for feminism as an organized movement,” Kellow said. “She didn’t see herself as a great feminist character breaking down doors for the sisters. I don’t think she was a keen mentor to other women.”

As the 1970s drew to a close, Mengers became a person out of time. The golden age of personal, edgy filmmaking that birthed “The Godfather” and “The Last Picture Show” became Reagan-ized, replaced by glossy, elbows-free movies that didn’t jive with Mengers’ caustic sensibility.

There was another fatal flaw. An inability to identify actors on the cusp of breaking through caused Mengers to make the wrong call on up-and-comers like Richard Gere, Jessica Lange and Arnold Schwarzenegger.

“You have to be able to spot and develop talent or you can’t build the next generation of stars,” Kellow said. “She was so much like Pauline Kael in that she was so deeply connected to the creative foment going on in the 1970s that when it was over and when it had changed, she was not interested in what was happening. She thought the people she represented had a right to go on forever.”

But it was Streisand’s defection in the early 1980s, after Mengers had pushed for her to appear in her husband Jean-Claude Tramont’s disastrous film “All Night Long,” that stung the most. Both women had come from hardscrabble backgrounds, lost their fathers at early ages and labored under difficult mothers, and Mengers made the mistake of seeing Streisand as more than a client.

“She thought she understood Barbra in a way no one else in Hollywood could,” Kellow said. “I just don’t think Sue ever thought Barbra would leave her, and it was the beginning of her own personal tailspin.”

In 1986 Mengers retired from the agency world. A comeback attempt in the late ’80s proved ill-advised; what followed were decades in the wilderness.

“It’s astonishing to me that someone of her intelligence and wit couldn’t find something else to channel her energies into,” Kellow said. “She could have become a producer or worked at a studio. She could have taught. But she was curmudgeonly and she viewed herself as Hollywood royalty that had abdicated.”

Despite his doubts, Kellow said the Mengers book was the most enjoyable experience of a career that’s been spent chronicling the lives of icons like Kael and Ethel Merman. He’s still searching for the subject of his next book and is busy shopping a screenplay he wrote with the playwright Michael Slade about Warren Beatty’s disastrous attempt to lure Kael to Los Angeles to be a studio executive. The divisive critic is a role he says he could see Joan Allen or Sally Field playing with relish.

As for Mengers, who died in 2011 at the age of 79, she is enjoying a renaissance she never lived to experience. Both Kellow’s book and “I’ll Eat You Last” have pushed the spotlight back in her direction. It’s a second act she would have loved.

“One of her friends told me, ‘She’d have been upset you were doing a biography of her,'” Kellow said. “The only thing that would have upset her more is if you weren’t writing one.”