After winning Wimbledon in 1968, the men’s champion, Rod Laver, walked away with $4,800. Billie Jean King, the women’s champion, left with just $1,800. At other events, the gap in pay was even wider. King — who won 129 career titles, including 12 Grand Slam single titles — fought to change that. As the dominant force in tennis at the time, she had the most to lose by spending time campaigning for reform rather than focusing solely on tennis. But she never lost sight of the bigger picture, and she turned her back on the U.S. Tennis Association as leader of the “Original 9” group of women who fought for gender equality in tennis. “We had one dream, and that was to create an opportunity where any girl — if she was good enough — could make a living playing professional tennis,” King, now 67, tells TIME. “Today they are living the dream, and we need to continue to make progress for all girls. Women from around the globe have chosen tennis as a career, and I am so proud of the champions in our sport as they truly embody our vision from 1970.” In 1973, King defeated former men’s No. 1 Bobby Riggs in a nationally televised matched dubbed the Battle of the Sexes. (Riggs, who played the role of male chauvinist rather well, had beaten Margaret Court in a similar televised match earlier that year and spent the interim taunting female players.) In 1981 King became the first professional female athlete to come out as a lesbian.