Mokgadi Caster Semenya OIB (born 7 January 1991) is a South African middle-distance runner and 2016 Olympic gold medalist. She won gold in the women’s 800 metres at the 2009 World Championships with a time of 1:55.45, the 2016 Summer Olympics, and the 2017 World Championships in her new personal best, 1:55.16. After the doping disqualification of Mariya Savinova, she also was awarded gold medals at the 2011 World Championships and the 2012 Summer Olympics, all in the 800 metres.
Semenya was “assigned female at birth, raised as a girl and identifies as a woman” but has XY chromosomes and exceptionally high testosterone levels (“hyperandrogenism”) due to a disorder of sex development.Following her victory at the 2009 World Championships, it was announced that she had been subjected to sex testing. She was withdrawn from international competition until 6 July 2010 when the International Association of Athletics Federations (IAAF) cleared her to return. In 2019, new IAAF rules came into force preventing women such as Semenya from participating in 400m, 800m, and 1500m events unless they take medication to lower their testosterone levels.