(CNN) — In theory, Billie Jean King should have nothing left to prove.

A glittering haul of 39 grand slam titles across singles, doubles and mixed doubles is one of the greatest tennis careers of all time, but it was for her uncompromising pursuit of equality that she transcended the game.

King, one of the founders of the Women’s Tennis Association and who campaigned for equal pay, is a champion for marginalized communities. She’s been awarded the Presidential Medal of Freedom and the Congressional Gold Medal, and the women’s Federation Cup now bears her name.

King is revered as an icon, but she still has unfinished business. At the age of 81, she’s gone back to college and hopes to graduate in May.

As an octogenarian, she’s a senior in more ways than one.

“In those days, women did

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