Answer by taking a quote from the following article:

King was born in Long Beach, California, into a conservative Methodist family, the daughter of Betty (nee Jerman), a housewife, and Bill Moffitt, a firefighter. Billie Jean's family was athletic. Her mother excelled at swimming, her father played basketball, baseball and ran track. Her younger brother, Randy Moffitt, became a Major League Baseball pitcher, pitching for 12 years in the major leagues for the San Francisco Giants, Houston Astros, and Toronto Blue Jays.

King's triumph at the French Open in 1972 made her only the fifth woman in tennis history to win the singles titles at all four Grand Slam events, a "career Grand Slam." King also won a career Grand Slam in mixed doubles. In women's doubles, only the Australian Open eluded her.  King won a record 20 career titles at Wimbledon - six in singles, 10 in women's doubles, and four in mixed doubles.  King played 51 Grand Slam singles events from 1959 through 1983, reaching at least the semifinals in 27 and at least the quarterfinals in 40 of her attempts. King was the runner-up in six Grand Slam singles events. An indicator of King's mental toughness in Grand Slam singles tournaments was her 11-2 career record in deuce third sets, i.e., third sets that were tied 5-5 before being resolved.  King won 129 singles titles, 78 of which were WTA titles, and her career prize money totaled US$1,966,487.  In Federation Cup finals, King was on the winning United States team seven times, in 1963, 1966, 1967, and 1976 through 1979. Her career win-loss record was 52-4. She won the last 30 matches she played, including 15 straight wins in both singles and doubles. In Wightman Cup competition, King's career win-loss record was 22-4, winning her last nine matches. The United States won the cup ten of the 11 years that King participated. In singles, King was 6-1 against Ann Haydon-Jones, 4-0 against Virginia Wade, and 1-1 against Christine Truman Janes.  In 1982, King was 38 years old and the twelfth-seed at Wimbledon. In her third round match with Tanya Harford of South Africa, King was down 7-5, 5-4 (40-0) before saving three match points to win the second set 7-6(2) and then the third set 6-3. King said in her post-match press conference, "I can't recall the previous time I have been so close to defeat and won. When I was down 4-5 and love-40, I told myself, 'You have been here 21 years, so use that experience and hang on.'" In the fourth round, King upset sixth-seeded Australian Wendy Turnbull in straight sets. King then upset third-seeded Tracy Austin in the quarterfinals 3-6, 6-4, 6-2 to become the oldest female semifinalist at Wimbledon since Dorothea Douglass Lambert Chambers in 1920. This was King's first career victory over Austin after five defeats and reversed the result of their 1979 Wimbledon quarterfinal. King said in her post-match press conference, "Today, I looked at the scoreboard when I was 2-0 in the third set and the '2' seemed to be getting bigger and bigger. In 1979, when I was up 2-0 at the same stage, I was tired and didn't have anything left. But today I felt so much better and was great mentally." Two days later in the semifinals, which was King's 250th career match at Wimbledon in singles, women's doubles, and mixed doubles, the second-seeded Chris Evert defeated King on her fifth match point 7-6(4), 2-6, 6-3. King was down a set and 2-1 in the second set before winning five consecutive games to even the match. King explained that she actually lost the match in the first set by failing to convert break points at 15-40 in the second and fourth games.  She reached the semifinals in her final appearance at Wimbledon, losing to Andrea Jaeger 6-1, 6-1 after beating Kathy Jordan in the quarterfinals, seventh-seeded Wendy Turnbull in the fourth round, and Rosemary Casals, her longtime doubles partner, in the third round. Jaeger claims that she was highly motivated to defeat King because King had defeated Turnbull, a favorite of Jaeger's, and because King refused a towel from an attendant just before her match with Jaeger, explaining, "I'm not going to sweat in this match."  King became the oldest WTA player to win a singles tournament when she won the Edgbaston Cup grass court tournament in Birmingham at 39 years, 7 months and 23 days after a straight-sets victory in the final against Alycia Moulton. The final official singles match of King's career was a second round loss to Catherine Tanvier at the 1983 Australian Open.  Before the start of the open era in 1968, King earned US$100 a week as a playground instructor and student at Los Angeles State College when not playing in major tennis tournaments.  In 1967, King criticized the United States Lawn Tennis Association (USLTA) in a series of press conferences, denouncing what she called the USLTA's practice of "shamateurism", where top players were paid under the table to guarantee their entry into tournaments. King argued that this was corrupt and kept the game highly elitist. King quickly became a significant force in the opening of tennis to professionalism. King said this about the amateur game,  In America, tennis players are not people. If you are in tennis, you are a cross between a panhandler and a visiting in-law. You're not respected, you're tolerated. In England, you're respected as an artist. In Europe, you're a person of importance. Manuel Santana gets decorated by Franco. The Queen leads the applause. How many times have I been presented at the White House? You work all your life to win Wimbledon and Forest Hills and all the people say is, "That's nice. Now what are you going to do with your life?" They don't ask Mickey Mantle that. Stop 12 people on the street and ask them who Roy Emerson is and they're stuck for an answer, but they know the third-string right guard for the Rams. I'd like to see tennis get out of its "sissy" image and see some guy yell, "Hit it, ya bum" and see it be a game you don't have to have a lorgnette or a sash across your tuxedo to get in to watch.

What else did she do?
King quickly became a significant force in the opening of tennis to professionalism.