Of all the events at the Olympics, the most challenging is the decathlon – a gruelling set of ten events held over two days: 100-metre race, long jump, shot put, high jump, 400-metre race, 110-metre hurdles, discus throw, pole vault, javelin throw and 1500-metre race. And the winner of this event, not surprisingly, gets to be called "The World’s Greatest Athlete".

The winners of the decathlon over the years have included legendary figures such as Jim Thorpe, Daley Thompson, Bob Mathias and Rafer Johnson. But few have captured the public imagination like Bruce Jenner, who won the gold 40 years ago at the Montreal Olympics in 1976.

Jenner’s victory had all the elements of sporting mythology: He won thanks to a dramatic finish in the final 1,500-metre event. He set a new world record. He humbled his Russian arch-rival, Mykola Avilov (the favourite, who had won the gold at the previous Olympics). And he was the man who, quite by chance, started the tradition of celebrating a victory by waving one’s country’s flag – something he did instinctively after taking a United States flag from a spectator in the adrenalin-rush of the moment.

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Hollywood hero?

With his rugged good looks, his sculpted 6' 2", 200-lb physique, and his seeming machismo, Jenner became an icon of American masculinity. And he seemed all set for a career in Hollywood, in the footsteps of other Olympic gold medallists such as Johnnie Weismuller, who had played Tarzan, and other muscular roles, over a quarter of a century.

Indeed, when the movie Superman was being made, Jenner was said to be a favourite for the role, until it finally went to Christopher Reeve. But whether he got that role or not, the point was that Bruce Jenner was Superman.

He was featured on the covers of several magazines (including Playgirl) and, in the ultimate honour given to any American sportsman, appeared on the pack of the breakfast cereal Wheaties, "The Breakfast of Champions".

Four years later, in the 1980 Olympics, Jenner’s decathlon record was bettered by the great Daley Thompson. But Jenner had by then moved on in life. He first made a high-profile career for himself on TV, and ultimately became a successful racing car driver. He was married three times (to a series of glamorous women including Elvis Presley’s former girlfriend Linda Thompson, and Kim Kardashian’s mother Kris Kardashian). He fathered six children. And then, as the years passed, he began to fade from the public memory.

Until 2015, that is.

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A man by mistake

Suddenly Bruce Jenner was splashed all over the US media once again, but this time in a rather different avatar – as "Caitlyn Marie Jenner".

Jenner confessed that his life had been one big sham. Since childhood, he said, he had seen himself as a girl who had been born as a boy by mistake. Winning the Olympic decathlon had just been one way of trying to resolve the issue, and prove to himself that he was indeed a man.

But, unfortunately, it didn’t work. He described the day after winning the Olympics gold: he had stood in front of the mirror naked, wearing only his gold medal, and felt a wave of despondency pass over him. Nothing had changed: he was still just the little girl who had been born a little boy by mistake. He said he had stared at his image in the mirror and asked himself desperately, “Now what do I do?”

It’s a condition that’s clinically termed gender dysphoria, and it’s usually a sad story of confusion, shame and dishonesty with oneself. Ever since Bruce Jenner was a kid, it turned out, he had secretly worn his sister’s and mother’s clothes. But now he started to wear a bra and panties under his own clothes, regularly, in an effort to keep in touch with his true gender.

Over the years, Jenner progressively moved on to having hormonal therapy, having his facial and body hair painfully removed, and having his Adam’s apple surgically reduced to match his inner female identity. He would wake up at 4.30 am and wear a woman’s dress and jewellery around the house; it was the only time of the day when nobody was looking, and he could really, truly be himself.

An entire life wasted?

But then one day, when he was in his 60s, Jenner asked himself what it would be like to be on his death-bed, and get the feeling that he had wasted his entire life. And that’s when he decided that he would finally become the person he was always meant to be: Bruce Jenner would make the public transition to Caitlyn Marie Jenner.

The coming out happened with Jenner revealing in a TV interview that she had now had a round of cosmetic surgery and officially become a woman.

As a result Jenner became one of the most googled names of 2015. She was also shortlisted for Time magazine’s Person of the Year for the bravery of that decision (she ultimately didn’t make it, but was listed in the "Time 100"). There was also, of course, a spate of insensitive jokes, ranging from the knee-jerk reflex pun about "Jenner-Bender" to the politically incorrect suggestion that if Bruce Jenner had been featured on the Wheaties cereal pack, Caitlyn should now be featured on the Froot Loops pack.

What Jenner has achieved is to make us ask questions of ourselves.

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The luck of the draw

The point of this story is the ambiguity of gender. After all, if the man supposed to be “the world’s greatest athlete” was in truth a woman (as indeed he turned out to be), who can be entirely sure of their own masculinity or femininity?

It is now commonly accepted by biologists that there is no fixed binary system of male and female. What we have instead is a spectrum, with various possibilities in between. How many possibilities, exactly, is a matter of conjecture: biologically speaking, probably six, involving differing configurations of the X and Y chromosomes.

While women are typically XX, men are typically XY – but then you can have have other varying combinations, ranging from XXY (one in 750 persons, approximately) to XXXY (one in 30,000 persons). It could happen to anyone; it’s simply the luck of the genetic draw.

To complicate matters further, there is the possibility that your body, your brain, and/or your reproductive system could all belong to different biological sexes.

Which is where we get into the distinction between sex and gender.

While sex is a matter of biology – a configuration of chromosomes, hormones, and anatomy, external and internal – gender, on the other hand, is about your inherent sense of who you are. And that could be masculine, or feminine, or neither, or both. Nor is it entirely clear that this is something you're born with, or develop in the course of your life.

As a result of all this, you could very well be a woman with a penis.

Or a man with a vagina.

Yes, it is complicated.

And some people are making it even more complicated. For example, New York City now officially recognises 31 different genders. No. 1 on that list is "Bi-gendered", followed by "Cross-dresser", "Drag-king", "Drag-queen", "Femme queen", "Female-to-male", "Gender-bender", "Genderqueer", "Male-to-female", and others. "Woman" and "Man" come in at at No. 16 and No. 17, respectively.

Facebook, meanwhile,offers you a choice of at least 51 different genders (motivated, at least partly, by self-serving ad targeting objectives), including "gender fluid", someone who supposedly has a dynamic understanding of their gender, moving between categories at will.

OK, so let’s talk about you now.

Are you a man? Or a woman?

Really?

Are you quite sure?

Caitlyn (formerly Bruce) Jenner would suggest you think carefully about it.