LONDON -- The movie about Billie Jean King and her match against Bobby Riggs in 1973, about what was -- at the time and maybe now -- the most famous moment of a great American life, has its premiere in London on Sunday. Emma Stone plays Billie Jean. Steve Carell plays Riggs. It's called "Battle of the Sexes," just because that's what King vs. Riggs was, a tennis match that rallied and roused and inspired women at that time in America.

Especially young women.

"It's not a documentary," Billie's longtime partner Ilana Kloss, says at their rented apartment on Somerset Road, right around the corner from a back entrance to the All England Club. "It's not a tennis movie. It's an amazing tribute to Billie and what she went through as she got a platform to change the world."

Ilana, a former professional player herself, pauses and says, "It's about the essence of that time."

"Yeah, the essence of a time about a match I never wanted to play," Billie Jean calls out from across the room. "But then Margaret [Court] lost to [Riggs]. I kept telling her, 'Margaret, you cannot lose to this guy.' Told her she could … not … lose. But then she did."

Margaret Court played Riggs first, after Billie Jean had originally turned him down. Riggs dusted her in straight sets in May of '73. He was 55 at the time. Billie Jean was about to turn 30, and still the best women's tennis player in the world. She had spent so much of the decade before the match fighting for women's rights, in professional tennis and everywhere else. It was because of the force of her talent and will that women's players finally had their own professional circuit, sponsored by Virginia Slims. But now here came Riggs, who'd once won the singles, doubles and mixed doubles at Wimbledon the same year, 1939, four years before Billie Jean King was born; here came Riggs to mock women and women's tennis and promote himself into what would finally become a $100,000 winner-take-all match at the Astrodome that 50 million people would watch on television.

"Margaret lost," Billie Jean King says now, the first week of another Wimbledon. "So I had to win."

She beat Riggs in straight sets that night. It is still the highest rated tennis match of all time on television. Now they've made a movie about it, about one made-for-TV event that really did give Billie Jean King a platform to keep changing the world. She will turn 74 in November. Forty-four years later, she does not stop. Truly, hers does continue to be one of the great American lives. Not just a tennis life. Not just the life she has had in business, and in the world of politics and activism. Not an American life defined by her gender. Just a truly great American life.

She has been just about everything up until now except a feature film. It figures that when she does become one, an Academy Award-winning actress is the one who gets the part. Billie Jean has been awarded the Presidential Medal of Freedom. The capital of her sport in America has her name on it: The Billie Jean King National Tennis Center in Flushing, Queens. She campaigned for her friend Hillary Clinton in 2008 and did it again last year and hates so much of what she has seen and heard since the last election. Last summer at Wimbledon she joked that Donald Trump was Riggs and Hillary was her. It is no joke to her now, especially because of things the new president keeps saying about women.

"He is," she says, "sending such a horrible message."

I ask her now, a long way from New York City, which has been her adopted home for a long time, what she thinks about her country these days.

"I don't think we have a moral compass," Billie Jean King says. "You look around and all you see and hear is that the only people who are truly golden in our country are the ones with the most money. I don't know what other people might be seeing. But what I'm seeing is a country and a world that's more about outer success and less about things that truly matter than ever."

She is up now, and pacing, on legs that have seen two knee replacements and eight surgeries total on those knees. It has never taken much to get her going, the fireman's daughter who came out of Long Beach, Calif., to change the world.

"You know what drives me crazy?" she says, voice rising. "When people talk about the good fight after they lose one. Let's stop talking about the good fight. I didn't get into tennis to just fight the good fight! Kumbaya is not going to get anybody across the finish line. If we're going to change things, we've got to do more than fight."

Above the entrance to Centre Court at Wimbledon is the famous Rudyard Kipling line: "If you can meet with triumph and disaster and treat those two impostors just the same." Billie Jean professes her undying love for Kipling, but says that the idea of anybody buying into that notion before a match is "full of s---t."

One of the things to which she has attached her name to is the Billie Jean King Leadership Initiative because, let's face it, who knows more about leadership or initiative than she does? She laughs now around the corner from Wimbledon, the day's play scheduled to begin in about half an hour.

"I want men involved!" she says. "You ever notice how women are the only ones who go to conferences?"

She's always laughed when I've suggested that she's the one who should have run for office, a long time ago, talking about what her life was like in the '70s and '80s when the world first found out she was gay. Of course, things were different then in the world she was trying to change. But she's the one who would have made a hell of a first woman president. No one ever had to wonder about what her message has been, about equal pay and equal rights and fairness.

And then Billie Jean King, one of the great champions America has ever produced in anything, is talking about tennis.

She is talking about her last Wimbledon singles title, in 1975, when she was 31, and how proud she still is that she and her friend Arthur Ashe, who was born the same year she was, both won the singles that year. Two American tennis players, one a woman and one African-American, who lived lives away from the court full of dreams and purpose and courage and possibilities. She is talking about the current sad state of the American game.

And then about her own game.

"My goal," she says, "is to play again."

Every year when she rents this place at Wimbledon, she rents an exercise bike. It is behind her, and to her right, in the corner. She talks about the surgeries to her knees. The scars are there, both knees and both sides, to plainly see. She talks about a bad shoulder and a bad foot. Ilana tells about how seven years ago at Wimbledon, after the knee replacements, when she, Ilana, was getting ready to play a veterans doubles match and then there was Billie Jean King -- in a blue warmup in the place where the dress code is famously white -- out on the court, just wanting to hit a few balls. Which she did.

"I wanted the feel the ball on the strings," she says, smiling, the tennis girl she once was doing the talking now. "Do you know what that feels like? But it's not just that. It's everything. The hand-eye in tennis, moving your feet, changing direction. God, I miss all that."

She talks about how there was a morning this year, right after New Year's, on a court at Randall's Island, when she was on the court and hitting balls for just 10 minutes. And happy.

"I don't care about competition," Billie Jean King says. "I've already had that."

She smiles.

"I just want to hit the ball," she says.

Everything she is, everything she's done, everything she still wants to do, started with that.