Billie Jean King transformed women's tennis into a professional sport. When she won her first Wimbledon singles title in 1966, the prize was a gift certificate for clothes. King's response was to begin a campaign, along with leading men's tennis players, to demand prize money at all U.S. Lawn Tennis Association tournaments. Five years later she was the first woman to earn $100,000 in a year as a professional tennis player. Rod Laver, the leading money winner on the men's tour, won $290,000 that year, suggesting the next inequity King challenged. In 1972 she complained loudly when she received only $10,000 for winning the U.S. Open, while male champion Ilie Nastase received $25,000. The women deserved parity, she argued, and they got it. Margaret Court won the U.S. Open in the first year of parity, as least partly because King was exhausted by September...