Beginning in extreme close-up on Joan River’s nude face as she’s made up for the day, you immediately understand that Joan Rivers: A Piece of Work is a film about the Joan we never get to see, the naked underbelly, the truest side of someone who has been reduced to a string of recycled plastic surgery potshots.

From the makeup chair, the cameras follow Rivers into the bowels of a comedy club basement where she mounts the stage in front of an adoring audience to unleash some bile. Younger audiences, the ones who only think of her as the crazy red carpet lady, might not know, and many others have forgotten, just how influential she’s been in the comedy world. But lest we forget, Joan, along with Phyllis Diller, was one of the first female comics to not only infiltrate the typically male-dominated comedy scene, but slap it around and make it her bitch. There would be no Sarah Silverman or Kathy Griffin (who makes a later appearance) without Rivers. Brimming with unimaginable energy, the only thing that betrays her age (keep the facelift jokes to yourself, peanut gallery) are her slightly slow movements as she makes her way down the stairs. But once she’s in front of the audience, you’d never imagine you’re watching a 75-year-old woman as she tears through a set that’s vulgar, uncompromising and hysterically funny.

Rivers on stage is as magnetic as the offstage persona documentarians Ricki Stern and Anne Sundberg (The Trials of Darryl Hunt, The Devil Came On Horseback) were able to capture. Invited inside Rivers’ apartment, a garishly decadent existence that looks like what would happen if Marie Antoinette and Liberace decided to go into interior decoration, audiences are given a glimpse into the daily life of a woman whose tireless efforts have cultivated a career spanning five decades. Panning a wall of drawers where jokes are kept in a system like Dewey Decimal library cards, Rivers has catalogued every funny thought she’s had over the years. As the camera pans, you see categories like “Cooking to Tony Danza” and “New York to No Self-Esteem.” For her, happiness is a packed schedule in her day planner. “That’s fear,” she says, pointing to an empty page a few months away.

While tragedies from her life, like her husband’s suicide, are touched on, the film’s real drama and intrigued comes from this fascinating glimpse into the comedienne’s inner life.

Grade: B+

Joan Rivers: A Piece of Work releases in select theaters June 11.