Betsy West and Julie Cohen knew they had a “great story” when their documentary about Supreme Court Justice Ruth Bader Ginsburg was released in America. But even they admit to being surprised when the low-budget May release, RBG, broke into the top 10 at the US box office in blockbuster season. When it closed in October, the film had taken just over $14 million.

“We thought it would do well,” says Cohen, “but not that well.” “It was, like, woah!” exclaims West.

To be fair, Ginsburg, a two-time cancer survivor and one of only four liberal-leaning justices left on the nine-person Supreme Court panel, is no ordinary 85 year old. The co-directors started talking about making the film in 2015 because of her growing internet celebrity as a result of some powerful dissents she had written in 2013 and 2014. “All of a sudden, young people were starting to go a little crazy for RBG [the woman], which already seemed interesting, and kind of funny,” says Cohen.

Millenials transformed Ginsburg into a meme-driven cultural icon, photoshopping her face onto images of Gal Gadot’s Wonder Woman and Scarlett Johanssen’s Black Widow character from the Avengers movies; quoting her dissenting opinions; and nicknaming her The Notorious R.B.G. after her fellow brooklynite, the late rapper Biggie Smalls, a.k.a. The Notorious B.I.G.

Books, videos, merchandise including mugs, jewellery and T-shirts, and Saturday Night Live all added fuel to the phenomenon. When she gives talks, her fans, who await the justice’s laser-like dissents with eager anticipation, fete her like a rock star. And she’s also the subject of a feature film On The Basis of Sex, released in the Uk in February.

Although quiet and reserved, she clearly enjoys her notoriety. In one of the most memorable moments of RBG, Ginsburg works out withpress-ups, planks, and weights wearing a sweatshirt with ‘Super Diva!’ emblazoned across the front.

The filmmakers had read about her routine in interviews, but actually seeing that Ginsburg could do what she claimed was a relief. “We didn’t know if it would live up to the hype,” says West. “But it did.”

Audiences at screenings they attended often applauded and little wonder: the veteran jurist is the leader of the resistance against the conservative majority on the Supreme Court bench, so seeing her in such fine fettle would have been reassuring to progressives. Last month, Ginsburg fractured three ribs in a fall, causing a collective nervous breakdown. Although she has since returned to work, reactions to the incident highlighted the fear that Trump will get a third nomination on the bench.

With the stakes so high, one can only imagine the pressure Ginsburg must feel under to carry on. Not that she has ever publicly expressed a desire to retire, even though some people urged her to under Trump’s predecessor.

“There was a suggestion, ‘Why doesn’t she step aside now that Obama’s still President?’,” says West. “But, you know, that didn’t work out so well. Obama was unable, in his final year, to get a Supreme Court Justice even considered, let alone approved.

“So she really would have had to step down when she was in her late 70s in order to have guaranteed an Obama appointed successor. And she says that she feels it’s a lifetime appointment and she will do it as long as she’s capable.”

She has always been a fighter, and West and Cohen put her groundbreaking work before becoming a Supreme Court Justice the heart of the documentary. They had interviewed her, separately, years earlier, for other projects, says Cohen, and “understood that the people who were celebrating her dissents weren’t actually aware of what she achieved for equal rights for women under the law when she was a lawyer in the 1970s, because it is not widely known even in the US”

Growing up as the daughter of Russian immigrants who had been excluded from education in their motherland because they were Jewish, Ginsburg learned about the effects of prejudice from an early age. While the documentary only touches lightly on the impact of her parents’ experience, “We almost saw that as a launching pad for everything she fought for,” says Cohen.

“Justice Ginsburg would say that the discrimination her father faced as an immigrant, as an under-privileged person financially, and as a Jew, was some of her earliest knowledge of injustice.”

As a Jewish girl in Brooklyn, Ginsburg felt part of a community. But when the family went on car trips,they’d see signs saying, “No Dogs or Jews Allowed”.

“So she became aware of the fact there was discrimination in the United States,” says West.

This extended to the “big New York law firm world,” continues Cohen, where antisemitism played itself out in the kind of law it was acceptable for Jews to practice. “Jews were doing real estate law. Jews were doing tax law. Jews were doing labour law. But other areas, no.”

Not that this held Ginsburg back. She battled her way through sexism at Harvard Law School, where she was just one of nine women in a class of 500 men, only to later find that New York law firms didn’t employ women as lawyers.

Gender discrimination thus superseded antisemitism: “Because she was not only Jewish but also a woman,” says Cohen, “it was like, ‘Okay, there are no women at all in any of those firms, be they Jewish or Christian.’”

Ginsburg’s home life couldn’t have been more different, and can almost be seen as a model for the kind of society she envisioned. Unusually for the times, her husband, Martin (known as Marty), whom she’d met as an undergraduate at Cornell, treated her as an equal. Rather than being threatened by her intellect, he celebrated and bragged about it. And when her career took off, he happily stepped back, repaying her for the love and support she’d given him when he was diagnosed with cancer during their university days.

Marty’s parents were progressive New York Jews who believed in equality and women’s rights, says Cohen, and “they imparted those values to Marty, and Ruth was the beneficiary.”

Ginsburg didn’t let the bigotry of the law firms stand in her way. She took a strategic approach and, in 1963, accepted a professorship at Rutgers Law School, where she taught some of the first women and law classes.

In the 70s, spurred on by the example of Thurgood Marshall’s work fighting for racial equality in the 60s, she argued gender equality cases on behalf of the American Civil Liberties Union in front of the then all-male panel of Supreme Court justices. Most of them were blind to the discrimination women faced every day in many different areas of their lives; Ginsburg, who felt like “a kindergarten teacher”, made sure they could see it.

She won five out of the six cases she argued before the court, in the process of which she demonstrated how gender inequality hurts not only women, but everyone.

While lives were changed, the workplace could still be an uncomfortable place for women. One of the differences between Ginsburg’s time and the filmmakers’, says Cohen, is that while Ginsburg was from “a generation where women getting into the workplace to even have the opportunity to be treated like crap was difficult; they’re from a generation where women were getting into the workplace, and everything from everyday condescension to overt harassment was part of the experience.”

She claims that everyone she knows from when she started working in the 80s “has a bunch of stories that until the recent #metoo generation, if you told them to men they would be shocked. Like, ‘Oh, I can’t believe that happens.’ Yeah, well, it happens.”

Adds West: “We felt it was the price of entry. We just thought that that kind of harassment, you had to put up with it. And what were you going to do? Who were you going to go to? There were hardly any HR departments, and they would just look at you and say, ‘Oh, he asked you to give him a back rub in the office? What’s the big deal?’”

Significantly, they finished RBG in October 2017, just as the first allegations of sexual abuse against Harvey Weinstein were coming out, and #metoo was taking off.

“So the film was released into a changed atmosphere,” says West. “And I think women were really ready to hear this story of a feminist icon. Someone who had started the progress for women, even though it’s not yet finished.”

RBG is in cinemas from January 4