Witch. Monster. Evil-doer. Zombie. In “RBG,” a survey of Supreme Court Justice Ruth Bader Ginsburg’s impact on American law, documentary co-directors Julie Cohen and Betsy West open with a montage of insults endured by the 84-year-old judge. Audiences for this peppy portrait will dissent. To young fans who’ve slapped Ginsburg’s face on T-shirts, coffee mugs and a million memes, she’s a hero, icon, and rebel, the yas queen of the judicial branch better known for Kate McKinnon’s “Saturday Night Live” impersonation than her hard-fought feminist victories.

“RBG” colors in that knowledge gap, showcasing the Ginsburg who argued for equal rights in front of the Supreme Court before “SNL” was even on the air. This spry celebration reveals that the real Ginsburg is neither beast nor badass, but an even-tempered, soft-spoken mediator—not typically the traits that inspire rousing high-fives, but qualities that honor the slow, uphill slog of positive change.

How would Ginsburg describe herself? First, as a Brooklynite, just like the Notorious RBG’s nickname inspiration, The Notorious BIG. “We have a lot in common,” nods Ginsburg, regarding the platinum-selling rapper who was murdered 20 years ago in an unsolved drive-by assassination. She’s not joking, exactly. Ginsburg doesn’t joke. Her daughter Jane confesses that she used to keep a journal called “Mommy Laughed,” listing the rare moments she caught her mother cracking a smile. As for what else the two Notarati have in common, fans are fixated on their deaths — in Ginsburg’s case, they’re praying that she lives forever, which inspires Cohen and West to include several sequences of the 5-foot-1 grandmother pumping her 3-lb. barbells in a sweatshirt that reads “Super Diva.” No, she doesn’t do “girl push-ups.”

Ginsburg’s family calls her “Bubby” or “Kiki,” the latter she earned as a baby who kicked her mother in the womb. She’d also call herself the daughter of immigrants, and her parents shaped her to be half the person she became: hard-working, feminine, polite. They weren’t expecting her to be quite so careerist. Besides, when Ginsberg graduated in 1959, the Supreme Court had been exclusively male since the first “Oyez, oyez” in 1789. Any woman arguing a case before the judges had to walk up those marble steps, past the staring portraits of centuries of men, and boldly speak her mind.

But Ginsburg didn’t strike anyone as bold, at least not outwardly. A blue-eyed beauty with no problem getting dates, she was expected to be a wife. She married her college sweetheart, Marty, and stayed happily wed until his death in 2010. Back then, almost no women went to law school, let alone qualified to join the Harvard review — which she did, while raising a toddler and nursing Marty through testicular cancer.

“He was the first boy I ever knew who cared that I had a brain,” says Ginsburg. Their love affair is the best part of the film. During her confirmation hearing in 1993, the strictly private Ginsburg lit up while describing her husband’s respect for her career. The cameras capture his proud glow as he sits behind her. He was a charmer; she was ever serene. As a lawyer for the ACLU, her approach to swaying male judges was to talk to them like sensible people who would surely agree with her once they knew the facts. Ginsburg didn’t believe they hated women — they just didn’t think about them, and that was something she could change.

“RBG” can’t enter Ginsburg’s inner sanctum. It’s stuck on the steps, merely able to peek in and reveal that she’s a workaholic who loves opera. In a recent onstage cameo at the Washington National Opera, she relishes saying her snobbish character’s name — “Krrrrrrakenthorp!” she growls — and when she gets to the line, “Ours is a family wildly trumpeted,” she punctuates the last word as though to make a point about a president she’s confessed she dislikes. (The film concedes she probably should have kept that to herself.) Other details go unexplored, like the jingly ring Ginsburg wears on her left hand that dangles what look like five evil eyes. Perhaps someone could take that jewelry as proof of her wickedness. But this doc, and everyone likely to watch it, would never question her valor.