Who ever heard of a swimming champion who's allergic to chlorine?

Despite being the son of a talented Australian cricketer, as a boy Ian Thorpe was useless at ball sports (an affliction with which Heroes of Swimming sympathises; in fact, we wonder if Ian is also a rubbish dancer). Thorpe's older sister told him to come swimming with her instead, but he was allergic to chlorine and had to swim with his head out of the water. It didn't stop him winning his first race.

By the time he was 13, Thorpe was already more than six feet tall. He was also now putting his face in the water, and going extremely quickly: at 14, he ducked under the four-minute barrier for 400m freestyle, and a few months later he shaved that time down to 3:53.44 at the Australian Swimming Championships. It got him into the team for the Pan Pacific Championships as the youngest Australian swimmer ever to represent his country.

It seemed like every time Thorpe swam, he swam faster. He was also still growing, which must have been worrying for the fully grown swimmers he was already beating. He came home from the 1997 Pan Pacifics with silver medals from the 4x200m relay and the individual 400m freestyle. He looked nailed on – and was duly selected – for the 1998 World Championships in Perth. There, his big rival was fellow Aussie Grant Hackett. A couple of years older, Hackett had been dishing it out to Thorpe for a while, and must have had every expectation of doing it again. Thorpe, though, had other ideas.

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With 100m left to swim in the final of the 400m freestyle, Hackett was an extremely comfortable 2.29 seconds ahead. In swimming terms, a 2.29 gap over 100m is a lifetime: Heroes of Swimming's mum could hold a gap like that. At the 50-to-go turn, Thorpe had pulled it back to 1.53, and an honourable silver medal beckoned – but then he turned on the afterburners.

Thorpe's finishing burst, with a kick that looked like someone had attached an outboard motor to his feet, would soon be famous, but this was the first time it had been unleashed on the world stage. Thorpe came down that last length like a train, and Hackett had no answer. He was ahead all the way until the very last stroke of the race – at which point Thorpe touched the wall first. At 15 years and three months old, he was the youngest-ever male world champion.

That 1998 gold was the start of an amazing run of global titles and world records at the Commonwealth Games, World Championships and the Pan Pacific Championships. His victory over 400m at the Pan Pacifics in 1999 – where he smashed Hackett and the great South African Ryk Neethling, and bettered the world record by two seconds – stunned the swimming community. It was memorably described by the peerless Rowdy Gaines, himself a four-time Olympic gold medallist: "[Thorpe] went into a balls-out sprint at 250m, and I have never seen anything like that. I've been around swimming a long time, and it's the most amazing swim I've ever seen, hands down."

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Thorpe set another world record in the 200m freestyle, and the stage was duly set for the 2000 Sydney Olympics.

During the entire first week of the Games, in honour of Thorpe's massive feet, the path from the front door to the sofa at Heroes of Swimming Towers was traced by a set of size-17 footprints, cut out of paper and stuck to the carpet. You don't realise just how big size-17 feet are until you have to find enough paper to cut out 25 of them. Clive James wrote a memorable article about Japanese hero-worship of the great swimmer, revealing that his name was pronounced "Sopu" in Japan (a tag that's been preferred to the more commonly heard "Thorpedo" round our way ever since). By the time of the 400m final, things had reached fever pitch – not least because Australia, the host nation, hadn't yet won a gold medal.

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Sopu didn't disappoint. He led from the gun; by the finish, the only swimmer within metres of him was Italy's Massimiliano Rosolino. The same evening, Thorpe anchored the 4x100m freestyle team to victory over the Americans, who had never lost the event at the Olympics and had boasted they would "smash [the Australians] like guitars". He won a third gold in the 4x200m relay, and silver medals in the 200m freestyle and the 4x100m medley relay.

The Sydney Games started a period of near-complete domination. Between then and the next Olympics, Thorpe won nine individual and nine relay gold medals at major championships, and set multiple world records at a variety of distances. At the 2004 Athens Olympics, he was part of the 200m freestyle final, which was billed – surely a little prematurely – as "the race of the century". Thorpe lined up with Pieter van den Hoogenband, who had beaten him at this event in 2000, Grant Hackett, and swimming's newest superstar, Michael Phelps. Van den Hoogenband led to 150m at world record pace, but faded to let Thorpe come through and grab victory. Thorpe also won gold in the 400m freestyle and bronze in the 100m freestyle, making him the first athlete ever to win triple medals at 100m, 200m and 400m.

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Thorpe took a year out of swimming after Athens, but injury, illness and, crucially, lack of motivation turned that into retirement in 2007. He was still only 25. Thorpe said when he retired that he'd been thinking about leaving the sport for a while, but was worried about life without the safety blanket of training. An attempt to get back into swimming in time for the 2012 London Olympics failed: disappointing for Thorpe, but a treat for BBC viewers, who got to see him in the commentary seat, dispensing charm and wisdom in equal measure, throughout the aquatic programme. After the Games, he hosted free advice clinics for swimmers, organised via Twitter and without PR fanfare.

Like many child stars who do their growing up in public, Thorpe has struggled with life outside the bubble. He's been visited by serious bouts of depression and, perhaps as a result, the certainties and rhythms of the training and racing pools have always appealed. Thorpe talked recently about competing in the 2016 Rio Olympics: no crazy ambition, this – he'd be 33 years old, and far from the most-senior swimmer to win medals at the Games.

In April 2014, though, Thorpe contracted a serious infection after shoulder surgery. The outcome was not immediately sure, but it seems likely to have ended his hopes of a comeback – making this a good moment to celebrate the achievements of one of the world's greatest swimmers.