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 at 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.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She was withdrawn from international competition until 6 July 2010 when the International Association of Athletics Federations (IAAF) cleared her to return to competition.
In 2010, the British magazine New Statesman included her in a list of "50 People That Matter 2010".