Billie Jean King

The social pioneer who won 12 Grand Slam singles titles and founded the Women's Tennis Association in 1973 to fight for equal prize money, Billie Jean King famously defeated Bobby Riggs 6-4, 6-3, 6-3 in the Battle of the Sexes before 30,492 spectators at the Houston Astrodome in 1973 -- the most-watched tennis match in history with 90 million television viewers worldwide. She was the first female athlete in any sport to earn over $100,000 in a single year (1971).