epa05324071 South Africa's Caster Semenya (C) competes in the women's 800m race at the Mohammed VI IAAF Diamond League meeting in Rabat, Morocco, 22 May 2016. EPA/ABDELHAK SENNA

London – Caster Semenya will be one of the stars of the Rio Games but what looks likely to be an inevitable victory in the women’s 800m will also bring fresh controversy upon the 25-year-old South African.

She had been expected to run in the 400m as well but her coach Jean Verster confirmed on Friday that she would concentrate on her premier event. That will still be enough to make her the centre of an ethical minefield, however.

Her misfortune – and advantage – is that her body naturally produces much larger amounts of testosterone, which make her faster; much faster than her rivals and perhaps even fast enough to break the 800m record of 1min 53.28sec set by Jarmila Kratochvilova, of Czechoslovakia, more than 33 years ago in July 1983. Kratochvilova never tested positive for drugs but her record has long been suspicious.

Semenya’s best to date is 1min 55.33sec but there has often been a sense among those close to her that she has been holding back. Given her story, perhaps it is no wonder. At 18 she stormed to prominence by winning the 800m world title in the wake of the revelation she had undergone gender verification tests.

In other words, the athletics world governing body, the IAAF, had checked to see if she was really a man. She was then kept from running until 2010, when it was in effect ruled she was a woman with extreme testosterone levels. From 2011 she had to take testosterone-reducing medication for ‘fairness’ and then won a silver medal in London — not that the furore has ever really died down.

Semenya’s case is hugely complex, and this version of events necessarily simplifies it. But the debate over whether she should be competing has never gone away. And since another athlete – Indian sprinter Dutee Chand – won a Court of Arbitration for Sport case last year, it meant the IAAF lost any power to regulate testosterone in hyperandrogenic women.

Semenya has stopped taking the drugs, and simply got faster than ever.

She is, beyond doubt, a woman, one with a chemical make-up that is both her blessing and her curse, as these Games will show.

THE South African’s yearly personal bests in the 800m took a hit during the period when she had to take testosterone-reducing medication (in red). – Mail On Sunday