Michael Phelps will put the finishing touches on his glittering Olympic career in London, where the swimming superstar says he has nothing left to prove - but plenty to achieve.
"I don't think anything he could do or not do could change his legacy," longtime coach Bob Bowman said. "He's the greatest Olympian of all time today. He will be after this summer."
That's the title Phelps seized four years ago in Beijing, where his stunning sweep of eight gold medals in eight events gave him a career tally of 14 gold medals -- the most of any Olympian -- and two bronze.
Phelps won't try to replicate his Beijing feat in London, where it's far from guaranteed that a seven-event slate will yield seven golds.
For Phelps, however, London is about putting a final gloss on a career that has seen him mature from a restless kid who found an outlet for his energy in the water to a cross-over star with all the trappings of modern celebrity.
"I just want to go out and challenge myself," Phelps said. "There are things that I want to do, and from a competitive part of my career I don't have a very big window to be able to accomplish them."
Just what those goals are Phelps is keeping to himself, but a peek at the record book offers a few clues.
His four individual events in London -- the 100m and 200m butterfly and 200m and 400m individual medleys -- all offer him a chance at a third straight Olympic gold.
No male swimmer has won the same Olympic event at three successive Games, although two women -- Dawn Fraser and Krisztina Egerszegi -- have done it.
Phelps also has a chance to surpass Soviet gymnast Larisa Latynina's record 18 career Olympic medals, amassed from 1956-1964.
For a time after Beijing, it wasn't clear if Phelps would get serious shot at those milestones.
A tabloid photo fracas in 2009, when a British paper ran a picture of him with a marijuana pipe, created an outcry that him reconsidering his plans to continue swimming through 2012.
Even after his mind was made up, Phelps found himself paying the price for his indecision and lack of motivation in training as rivals such as US team-mate Ryan Lochte surged to the top of the sport in 2010 and 2011.
"Two years after Beijing, it was pretty clear that I wasn't doing everything that I could do," said Phelps, who believes he and Bowman have made up for lost time well enough for him to make an impact in London.
Certainly Phelps has overcome adversity and negative publicity before.
After winning six gold medals and two bronze at the 2004 Athens Olympics he weathered controversy over an underage drink-driving charge. And he soldiered on after a broken wrist disrupted his preparations for Beijing.
In some ways, the upheaval and unexpected defeats of the past few years have removed the pressure for perfection and given Phelps time to look back at the entire arc of his Olympic career.
That started in 2000, when he made the team for Sydney at 15 and finished fifth in the 200m butterfly.
Bowman recalled that Phelps headed out to race in Sydney without properly tying his swim suit.
"I was obviously not all together, I wasn't fully engaged in everything that I was doing," Phelps recalled of his first Games.
Then came Athens, where talk of matching Mark Spitz's record of seven golds at one Games had begun but Phelps was more interested in testing himself against heavyweights Pieter van den Hoogenband and Ian Thorpe in the 200m free, a race that yielded bronze.
"I wanted to get in there with the best -- and we kind of learned that I could juggle a bunch of different things," he said.
In Beijing, Phelps recalled, "everything had to be perfect," giving him little time to appreciate his own accomplishment.
"It's a bunch more relaxed, laid back," Phelps said of his preparations for London, although the famously intense racer still cleary has his sights on gold.
"There is no need to put yourself out there if you don't know if you can really do it," he said.