Mokgadi Caster Semenya OIB (born 7 January 1991) is a South African middle-distance runner and 2016 Olympic gold medalist. Semenya won gold in the women's 800 metres at the 2009 World Championships with a time of 1:55. 45 and at the 2017 World Championships in her new personal best, 1:55. 16. Semenya also won the silver medal at the 2011 World Championships in the 800 metres. She was the winner of the gold medal in the 800 metre events at the 2012 Summer Olympics and 2016 Summer Olympics.