But then he hits the water and the other Michael Phelps is revealed -- the one who has a realistic chance of equalling the greatest feat in Olympic history -- Mark Spitz's seven gold medals at one Olympic Games. The media frenzy surrounding the "next" Mark Spitz once followed Ian Thorpe but, since last year's world championships, where Phelps set five world records and won four gold medals and two silver, it has tagged the young American.
Unlike Thorpe, who is alternatively bored and irritated by the public fixation on his medal tallies, Phelps has not tried to avoid the question. He has embraced the hype and the accompanying pressure, saying it inspires him to do things that no one else has done.
"It's exciting for me," he says. "I don't think there's a down side at all."
But he has also set his public goal for the Athens Games at one gold medal, reasoning that he went home from Sydney with nothing as a 15-year-old. Whether that will be enough for an American public primed to expect fistsful of gold, is another matter.
There is nothing in Phelps' background to suggest the juggernaut that he has become, just as there was nothing in Thorpe's happy middle-class childhood to mark him for brilliance.
Phelps' upbringing was less comfortable in Towson, a former mill town on the northern fringe of Baltimore, once described as the murder capital of the United States. His father Fred, a state trooper, and mother Debbie, a school administrator, split when he was seven. Debbie brought up their three children, Hillary, Whitney and Michael, her youngest.
He followed his sisters to the swimming pool and never left. Like Thorpe, he has an older sister (Whitney) who also represented her country, but whose Olympic dream was crushed by injury.
Whether it is related to his childhood circumstances or not, Phelps has a remarkable ability to disappear inside himself, to go to a place where all that exists is him and the water. "The water is my home," he says.
So fierce is his concentration, that his coach at the North Baltimore Aquatics Club, Bob Bowman, recalls having to "physically shake" Phelps out of his pre-race reverie as an 11-year-old to send him to the marshalling room so he didn't miss his race.
But that is not his only special feature. Phelps is a physical freak. His wingspan is substantially longer than his height, a characteristic he shares with another champion, Grant Hackett. Phelps is 192cm tall, but measures almost 200cm between his outstretched fingertips. Bowman believes the superior wingspan gives him a unique balance in the water.
He is exceptionally flexible, a requirement of all great swimmers, but Phelps has hyper-extension in his elbows and ankles. At 88kg he is a lightweight compared with Thorpe's 100kg, 195cm frame. And his size 14 feet do not come close to Thorpe's size 17.
But he has filled out noticeably in the past year. Bowman says Phelps may gain another couple of centimetres and kilograms as he reaches physical maturity.
Even his biochemistry is different. During the US Olympic trials, on his busiest night when he swam three races, sports scientists were amazed to see his lactic acid levels drop between his second and third races, indicating that he was actually recovering while racing the 100m butterfly.
With his physical attributes, he has an unmatched versatility, swimming backstroke, butterfly and freestyle at the highest level. Many swimmers are world-class in two strokes, but only he has three.
That has led to the unique program of eight events (two more than Thorpe) that he will take on in Athens. He qualified in six individual events, but trimmed the 200m backstroke from an already stuffed schedule.
Spread your wings: Michael Phelps is 192cm tall, but measures almost 200cm from fingertip to fingertip. This superior wingspan is said to give him a unique balance in the water.
PHELPS' PROGRAM
Today
400m individual medley
Tomorrow
200m freestyle preliminaries
4 x 100m freestyle final
Monday
200m butterfly preliminaries
200m freestyle final
Tuesday
200m butterfly final
4 x 200m freestyle final
Wednesday
200m individual medley
preliminaries,
200m butterfly final
Thursday
100m butterfly preliminaries
200m individual medley final
Friday 100m butterfly final
Saturday 4 x 100m medley relay
Sunday collapse
Thorpe and Phelps encompass almost the entire swimming program, swimming 14 events between them, but meet in just one
individual event - the 200m freestyle.
ThorpePhelps
AGE2119
HEIGHT195cm192cm
WEIGHT100kg88kg
SHOE SIZE1714