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.

Any information on how her career ended?