Billie Jean King poses for a portrait on Thursday, June 4, 2015 in New York. AP
In this September 23, 1970, tennis players hold up $1 bills after signing a contract with World Tennis magazine publisher Gladys Heldman to turn pro and start the Virginia Slims tennis circuit. From left standing are: Valerie Ziegenfuss, Billie Jean King, Nancy Richey and Peaches Bartkowicz. From left seated are: Judy Tegart Dalton, Kerry Melville Reid, Rosie Casals, Gladys Heldman and Kristy Pigeon. Gladys Heldman replaced her daughter, Julie Heldman, who was injured and unable to pose for the photo. Courtesy Houston Library
American tennis player Billie Jean King, right, President of the Women's Tennis Association (WTA), at a meeting with a committee of the the All England Lawn Tennis Club to discuss more equal prize money for male and female tennis players, Wimbledon, London, 26th February 1975. The meeting resulted in an increase in prize money for women from 70 to 80 per cent of men's prizes and the promise of an annual review. Getty Images
Julie Heldman of United States practices her serves for the 43rd Wightman Cup matches against Great Britain. Getty Images
14th June 1970: American tennis player Billie Jean King in action against Ann Jones of Great Britain during their Wightman Cup match at Wimbledon. Getty Images
Valerie Ziegenfuss. Getty Images
Peaches Bartkowiez In action at the 1970 Wimbledon Tennis Championships. Shutterstock
American tennis player Kristy Pigeon in action against Great Britain's Ann Jones in the London Grass Court Championships (later the Queen's Club Championships) at the Queen's Club in West Kensington, London, 18th June 1968. Getty Images
Australian tennis player Kerry Melville (later Kerry Reid) during a match against Judy Dalton (nee Tegart) at Wimbledon, London, UK, 28th June 1971. Getty Images
American tennis player Rosemary Casals playing Patricia Cody in the first round of the Rothmans Hard Court Lawn Tennis Championship at Bournemouth, 27th April 1970. Getty Images
Australian tennis player Judy Tegart in action at Bournemouth. Shutterstock
Nancy Gunter in action at a tournament in 1970. Shutterstock
Members of the "Original Nine" Billie Jean King, Jane "Peaches" Bartkowicz, Kristy Pigeon, Valerie Ziegenfuss, Judy Tegart Dalton, Julie Heldman, Kerry Melville Reid, Nancy Richey, and Rosemary "Rosie" Casals, who started the Women's Tennis Association, pose for a photo at the 40th anniversary of Family Circle Cup tennis tournament in Charleston, South Carolina April 7, 2012. Reuters
Billie Jean King poses for a portrait on Thursday, June 4, 2015 in New York. AP
In this September 23, 1970, tennis players hold up $1 bills after signing a contract with World Tennis magazine publisher Gladys Heldman to turn pro and start the Virginia Slims tennis circuit. From left standing are: Valerie Ziegenfuss, Billie Jean King, Nancy Richey and Peaches Bartkowicz. From left seated are: Judy Tegart Dalton, Kerry Melville Reid, Rosie Casals, Gladys Heldman and Kristy Pigeon. Gladys Heldman replaced her daughter, Julie Heldman, who was injured and unable to pose for the photo. Courtesy Houston Library
American tennis player Billie Jean King, right, President of the Women's Tennis Association (WTA), at a meeting with a committee of the the All England Lawn Tennis Club to discuss more equal prize money for male and female tennis players, Wimbledon, London, 26th February 1975. The meeting resulted in an increase in prize money for women from 70 to 80 per cent of men's prizes and the promise of an annual review. Getty Images
Julie Heldman of United States practices her serves for the 43rd Wightman Cup matches against Great Britain. Getty Images
14th June 1970: American tennis player Billie Jean King in action against Ann Jones of Great Britain during their Wightman Cup match at Wimbledon. Getty Images
Valerie Ziegenfuss. Getty Images
Peaches Bartkowiez In action at the 1970 Wimbledon Tennis Championships. Shutterstock
American tennis player Kristy Pigeon in action against Great Britain's Ann Jones in the London Grass Court Championships (later the Queen's Club Championships) at the Queen's Club in West Kensington, London, 18th June 1968. Getty Images
Australian tennis player Kerry Melville (later Kerry Reid) during a match against Judy Dalton (nee Tegart) at Wimbledon, London, UK, 28th June 1971. Getty Images
American tennis player Rosemary Casals playing Patricia Cody in the first round of the Rothmans Hard Court Lawn Tennis Championship at Bournemouth, 27th April 1970. Getty Images
Australian tennis player Judy Tegart in action at Bournemouth. Shutterstock
Nancy Gunter in action at a tournament in 1970. Shutterstock
Members of the "Original Nine" Billie Jean King, Jane "Peaches" Bartkowicz, Kristy Pigeon, Valerie Ziegenfuss, Judy Tegart Dalton, Julie Heldman, Kerry Melville Reid, Nancy Richey, and Rosemary "Rosie" Casals, who started the Women's Tennis Association, pose for a photo at the 40th anniversary of Family Circle Cup tennis tournament in Charleston, South Carolina April 7, 2012. Reuters
Billie Jean King poses for a portrait on Thursday, June 4, 2015 in New York. AP