When Serena Williams takes to the court at the Rio Olympics this month, the US tennis star won’t really be alone. She will have arrived at the Games with an entourage of paid staffers, coaches and sponsors who’ve helped her every step of the way.

Worth an estimated $150m in 2016 (more than any other female athlete, according to Forbes), Williams trains upwards of 30 hours per week, but has never had to work a second job to get by and pay her way in sport. She’s one of a small minority of Olympians.