Billie Jean King (b. November 22, 1943, Long Beach, CA) is an American former World No. 1 professional tennis player. King won 39 Grand Slam titles: 12 in singles, 16 in women's doubles, and 11 in mixed doubles. King won the singles title at the inaugural WTA Tour Championships. King often represented the United States in the Federation Cup and the Wightman Cup. She was a member of the victorious United States team in seven Federation Cups and nine Wightman Cups. For three years, King was the United States' captain in the Federation Cup.
King is an advocate for gender equality and has long been a pioneer for equality and social justice. In 1973, at age 29, she won the "Battle of the Sexes" tennis match against the 55-year-old Bobby Riggs. King was also the founder of the Women's Tennis Association and the Women's Sports Foundation.