It was 1955 in Los Angeles, eight years after Jackie Robinson broke Major League Baseball's color barrier and slammed the idea of equal opportunity into America's conscience.
Billie Jean Moffitt was told she couldn't pose for a picture at the Los Angeles Tennis Club with other young players because she wasn't wearing a tennis dress. Instead she wore tennis shorts her mother sewed for her.
Immediately, the 11-year-old knew she wanted things to change. But Billie Jean, who later married law student Larry King, saw that to foster change, she had to become No. 1 before she truly had a voice.
She was already on her way.
Initially, she just wanted to play football in front of her Long Beach, Calif., home with her little brother Randy. A few months earlier, her mother had urged her to stop playing that "boy" sport and to start acting more "ladylike." When a friend told her that in tennis she could run, jump and hit a ball, she picked up her first racket.
Billie Jean was in love with tennis from the start. She told her mother on the way back from her first lesson that she wanted to be No. 1 in the world and that playing tennis was what she wanted to do with her life.
She stayed completely focused on that goal and didn't have to wait long. By the time she was 17 and still in high school, she entered Wimbledon's doubles tourney with Karen Hantze, 18. They took the crown, the youngest team to do so.
"A champion has got to say to themselves, 'I want the ball no matter what,' and be willing to be at high risk. You just gotta do it," King said in the recently aired HBO documentary, "Billie Jean King: Portrait of a Pioneer."
In fall 1990, Life magazine honored her as one of the 100 Most Important Americans of the 20th Century. Babe Ruth, Muhammad Ali and Jackie Robinson were the only fellow athletes on the list. In 1972, she became Sports Illustrated's first female "Sportsman" of the Year.
At Wimbledon, where King won 20 titles (six singles, 10 doubles and four mixed doubles), she had a remarkable 224-41 record. She won 39 Grand Slams in her 24-year career and was the first woman to earn more than $100,000 in a single season, which she did in 1971.
For the next several decades after her first big triumph in 1961, King rallied for equal opportunities and equal prize money for female athletes in a time when the odds were against them. Her most famous win, 1973's Battle of the Sexes with Bobby Riggs, came the year after Congress' momentous decision to pass Title IX, a section of the Federal Education Amendments that mandated equal funding for men's and women's athletic teams.
King felt that losing the Battle of the Sexes, held at Houston's Astrodome and viewed by 90 million people, would jeopardize the advancements made with Title IX and give naysayers a reason to ignore women's sports.
"The political and personal stakes were so high that night in Houston that the normally impervious King threw up in the locker room beforehand," said Sally Jenkins, who wrote about King several times for Sports Illustrated.
"I always performed my best when the confrontation was most heightened, in the clutch," King wrote in her 1982 autobiography written with Frank Deford, "Billie Jean."
To King, there was no reason she should be treated differently as a woman. "I see the big picture first and go backward to execute it," King told Sports Illustrated in 1991.
Her ability to see that big picture was honed as a child. "Clyde Walker, her teacher at the Houghton Park public courts in Long Beach, thought teaching would help her game, so one afternoon she gave her first lesson (at 11 years old) to a group of younger children," wrote Jenkins in a 1991 SI article.
King, 62, has several methods she's relied on: rehearsal, ritual and repetition. She told one player that "practice equals spontaneity."
"You have to stay in the moment," she told Jenkins. "I always knew when I was going to play a great match because I woke up in the morning feeling everything. I was so alert. I could feel the water in my hair in the shower. I would pick up my tennis racket thinking of nothing but picking up my racket."
Seeing that more prize money was given to men than to women, she took action. King helped found the first women's circuit, signing a $1 contract with eight other women to play in the Virginia Slims tour.
In 1973, the Women's Tennis Association was born, followed the next year by World Team Tennis. In 1974, King became the first woman to coach a co-ed professional team, the Philadelphia Freedoms of World Team Tennis.
"In essence, I have to possess enough passion and love to withstand all the odds," King wrote in "Billie Jean." "No matter how tough, no matter what kind of outside pressure, no matter how many bad breaks along the way, I must keep my sights on the final goal, to win, win, win — and with more love and passion than the world has ever witnessed in any performance."
King realized that the Battle of the Sexes represented much more than just proving that a young woman could beat a 55-year-old man. Tennis champ Margaret Court was unable to do so earlier that year when Riggs challenged her to the first battle, for $10,000.
King won her battle 6-4, 6-3, 6-3, taking home $100,000.
"Beating a man wasn't really the important thing," said now-former husband Larry King in HBO's documentary. "The important thing was that women professional athletes deserved an opportunity to be as good as they could be, in whatever endeavor they chose. That's what won that night."
"I was a 14-year-old, male-chauvinist kid (who) hoped that Bobby Riggs would kick her (butt)," said four-time U.S. Open singles champ John McEnroe on opening night of the 2006 U.S. Open — the night the Open's home was renamed the USTA Billie Jean King National Tennis Center. "But now that I am a father of four little girls, I have to say for the record I'm glad Billie Jean King won.
"I don't think it's a stretch to say that Billie Jean King is the single most important person in the history of women's sports."
Chris Evert, who lost to King in the U.S. Open semifinals in 1971, said, "As great a tennis champion as she was, I don't even think about what she did on the court as much as how she'd had the vision to look ahead and see how far she could take not only women's tennis but women's sports."
"Her overall philosophy," Jenkins wrote, "is simple: When in doubt, attack."
"Tennis is not merely a game but a blueprint for constructive living. In her symbiotic, ordered view of the world, tennis is about fortitude — facing up to things — and the value of a good effort for its own sake," Jenkins said.

BY KASEY SEYMOUR