Japan's Naomi Osaka has surpassed Serena Williams as the highest-paid female athlete, raking in $37.4 million in prize money and endorsements over the last year, according to Forbes. The 22-year-old's total is most earned by a female athlete in a 12-month period. Maria Sharapova held the record for 12-month earnings among female athletes, having made $29.7 million in 2015.