From the moment she entered professional tennis Billie Jean King started to build a reputation as an equal rights advocate. She was a key instigator of the first women’s tennis tournament; organised in response to the huge difference between men and women’s prize money in professional tennis tournaments.

In 1973 she played a high profile tennis match against male tennis veteran Bobby Riggs. Riggs was outspoken in his opposition to women in tennis and insisted that he could never be beaten by a woman. Billie Jean thrashed him in straight sets 6-4, 6-3, 6-3.

But when her former secretary and travelling companion Marilyn Barnett filed a palimony suit against her in 1981, Billie Jean was a lot less upfront about her lesbianism. Still married to sports promoter Larry King at the time, Billie Jean publicly admitted to having had an affair with Barnett but also described it as “a mistake”. She also claimed that the case had strengthened her marriage.

Barnett lost her case in 1981 as well as a subsequent appeal, not because of any doubts about the affair but because it was ruled it had never constituted a contractual relationship. King, despite her statements playing down the lesbianism and bolstering her marriage, lost most of her commercial endorsements and had to postpone her retirement from tennis for financial reasons.

She has subsequently explained that she realised she was a lesbian as early as 1968 but couldn’t bring herself to admit it to her husband or her ultra-conservative parents. She finally came out publicly in 1998 and has subsequently worked as an advocate for LGBT rights and a campaigner against homophobia in sport.

In 2009 she received the Presidential Medal of Freedom. When presenting the award, President Obama said:

“Today we honor what she calls ‘all the off-the-court stuff’ – what she did to broaden the reach of the game, to change how women athletes and women everywhere view themselves, and to give everyone, regardless of gender or sexual orientation – including my two daughters – a chance to compete both on the court and in life. As Billie Jean once said, ‘We should never, ever underestimate the human spirit.'”