Sue Mengers, left, with her mother, Ruth: “Can I Go Now?” describes their relationship as fraught with tension and antagonism. (Personal collection of Sue Mengers, Courtesy of Joanna Poitier)

To call Sue Mengers a “character” is an understatement, unless the word is written in all caps, followed by an exclamation point and modified by an expletive. And based on Brian Kellow’s assessment in his thoroughly researched “Can I Go Now?,” even that description might be playing down her personality a bit.

Gutsy, pushy and savvy, Mengers was the take-no-BS power agent for many of Hollywood’s boldest bold-faced names in the late 1960s and the ’70s. A scrapper who worked her way up from low-level receptionist to high-profile celebrity rep in an industry largely dominated by men, she boasted a murderer’s row of high-profile clients, Barbra Streisand, Gene Hackman, Faye Dunaway, Peter Bogdanovich, Mike Nichols, Michael Caine and Candice Bergen among them. As a result, she became a star in her own right, throwing legendary dinner parties where her “twinklies” — her word for the shiniest A-listers — could make career connections while occasionally dabbling in controlled substances. She also was famous for having a tongue saltier than the rim of a margarita glass. This is a woman who landed actor Tom Ewell as a client after confirming that she could do something for him that other agents couldn’t: sleep with powerful Broadway producer David Merrick. (Note: She used another word for “sleep with.”)

Over the years, Mengers has been the focus of “60 Minutes” segments, magazine profiles and, after her death in 2011, a one-woman Broadway play called “I’ll Eat You Last” starring Bette Midler. But no one had written a book about her until now. Kellow, also the biographer of New Yorker film critic Pauline Kael, has interviewed so many of Mengers’s confidantes and industry colleagues that his list of sources — peppered with names like Streisand, Jack Nicholson, Cher, David Geffen and Robert Evans — takes up almost a whole page in the acknowledgments.

"Can I Go Now?: The Life of Sue Mengers, Hollywood's First Superagent" by Brian Kellow (Viking)

“Can I Go Now?” — a title inspired by something Mengers often said to cut short conversations — offers plenty of dishy, inside-’70s-Hollywood stories, including tales from those soirees at her Beverly Hills home, where bowls full of cocaine were regularly laid out on the tables. (“I was putting sugar in my coffee,” Michael Caine remembers of his first visit to Mengers’s residence, “and she said, ‘Don’t touch that. It’s cocaine.’ ”) Even Princess Margaret once let her royal hair down at La Casa de Sue. Despite an invitation from Nicholson, however, she did not partake of the powder in those bowls but did, according to agent Michael Black, get “a little sauced” and come on to John Travolta.

Though Mengers and the glitzy world she cultivated are remembered with great affection on these pages, Kellow doesn’t shy away from also highlighting her negative traits, qualities that often worked at odds with her strongest attributes. While great at orchestrating relationships — Mengers reportedly seated Ann-Margret next to Mike Nichols at one of her dinners, paving the way for the actress’s casting in “Carnal Knowledge” — she was often sloppy about the finer details of dealmaking. Her instincts could be on point — she cannily stole Ryan O’Neal from his existing agent in the immediate aftermath of the success of “Love Story” — but she also could be wildly off the mark in her decision-making. When client Burt Reynolds urged her to sign his then-girlfriend Sally Field, Mengers refused, then advised another client, Tuesday Weld, to turn down the lead in “Norma Rae,” a role that resulted in an Oscar — for Sally Field.

While she may have been a woman winning at what was traditionally considered a man’s game, she had no interest in feminism and sometimes made comments others considered racist, homophobic or anti-Semitic, even though she was Jewish herself. And despite her caustic manner, she could be extraordinarily sensitive; according to the book, Mengers never fully recovered after Streisand, her most prized client, dropped her as an agent in the early ’80s.

In other words, Mengers was a bundle of fascinating contradictions perpetually draped in one of her signature caftans. But the author only semi-successfully manages to reconcile all those facets into a cohesive portrait. The prose gets so mired in detail that it lacks vibrancy at times, a significant shortcoming in a book about someone so blindingly colorful. Given Kellow’s access to such superb sources and the frequency with which he quotes them, one wonders if “Can I Go Now?” might have been a more exhilarating read as an oral history rather than a work of narrative nonfiction.

As the 1990s dawned, Mengers retired as an agent, having lost much of her clout the way so many do in Hollywood: by having the audacity to age. But “Can I Go Now?” acknowledges that, even though she was often depressed in her later years, she continued to act as an under-the-radar influencer. She played a key role in persuading her old friend Streisand to star opposite Seth Rogen in the comedy “The Guilt Trip.” And as Kellow writes, she continued to host those parties filled with twinklies, inviting to her table such younger sparklers as Jennifer Aniston, Sean Penn, Jon Hamm and Tina Fey. (Fey even thanked Mengers by name in her 2008 Emmy acceptance speech.) Unfortunately, Kellow doesn’t spend much time exploring the impact she had on those and other contemporary stars, which makes it difficult to get a full sense of Mengers’s true legacy.

Former “Entertainment Tonight” reporter Barbara Howar says at one point in the book that she believes Mengers “had a mask.” Though he makes an admirable effort to remove it, Kellow gets only halfway there.

Jen Chaney is a pop culture critic and writer and author of “As If!: The Complete Oral History of ‘Clueless.’ ”

The Life of Sue Mengers, Hollywood’s First Superagent

By Brian Kellow

Viking. 326 pp. $27.95