He has spent his life demolishing records and building a stockpile of gold medals, but his final competition is looking more like a lap of honour than his crowning glory.

Phelps did that four years ago when he reached the summit of Olympic achievement by winning a mind-boggling eight gold medals in Beijing.

The problem was he soon discovered that perfection was flawed and no matter which direction he looked, he realised the only way forward was down. Whatever he does in London, Beijing will remain his defining moment.

"I don't think anything he could do or not do will change his legacy," said Phelps's lifelong coach Bob Bowman. "He's the greatest Olympian of all time today and I think he will be after this summer."

Phelps has entered seven events in London, one less than he swam in Beijing and Athens in 2004 and no one would ever rule out his chances of winning the lot again.

But in a sport where medals are won and lost by the tiniest numbers, the chances of him winning all seven look slim. While his main rivals are swimming faster, Phelps has not set a world record in over three years and his medal stacks are getting progressively lower.

At the 2009 world championships, he won five gold medals. In 2011, he won four, and the 27-year-old is resigned to the prospect that he may not win everything he enters in London.

"We've done a lot of cool, amazing, exciting things, and now it's just time to have fun," Phelps said. "We're relaxed. This is just about what size cherry I want to put on top of my sundae."

His main obstacle after Beijing was finding the motivation to get out of bed before dawn every day and churn through the thousands of laps he needed to stay at his peak.

A global sporting icon who has already amassed a fortune, he didn't need the money or the fame and the lure of adding a few more records to his CV started to lose appeal.

Although he holds the record for the most gold medals at a single Olympics (eight) and total (14), there are still some significant records within his reach.

He needs just three more medals of any colour in London to surpass the overall record of 18 held by Soviet gymnast Larisa Latynina.

If he medals in each of his four individual events, he will equal Latynina's career record of 14 individual medals.

And if he wins gold in either of the two medley or two butterfly finals, he will become the first male swimmer to win the same individual event at three Olympics.

"If I go out and do the best that I can and don't medal or get a bronze or a silver, at the end of the day there aren't many people that can say they have this," Phelps said.

"If somebody says it's a failure, I don't care. If I can say I've done everything I can and I've been happy with my career, that's all that matters."

Phelps partied hard after Beijing and his good boy image took a beating. He made regular trips to Las Vegas and in 2009, he was photographed with a pipe used to smoke pot.

He briefly toyed with the idea of quitting but rediscovered his motivation through the pain of defeat.

With his long arms and powerful legs, he is blessed with the perfect natural gifts to slice through the water as gracefully as a dolphin, but what sets him apart is the predatory instincts of a killer shark.

"I still want to win every race I go in," he said. "I've never, ever liked losing."

Phelps returned to training with renewed vigour, logging up to 70 kilometers (43 miles) a week and sleeping each night in a high-altitude chamber that was installed in his bedroom.

His results started to improve and he won four events at last week's U.S. Trials, ensuring that his final lap of honour will at least be a quick one.

"I'm still excited about the Olympics. It's the biggest stage to perform at," he said. "The experiences that I have had not only being on the national team but also the Olympic team have changed my life."

For Bowman, London is about the end of an unforgettable journey.

"I would like for us to be able to savour this experience and get all the best parts of it out again," said Bowman.

"However this ends up, it will be exactly the way he and I chose to make it end up.

"If it's good we made good choices, if it's not, probably could have done better, we will just think about the other ones (Olympics), they were pretty good."

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