Swimming phenomenon, legend, superstar, golden boy. Whatever you call this 23-year-old American, he has proved to be rather useful in the pool.
At Sydney in 2000 Phelps made the headlines when he became the youngest American male swimmer at an Olympics in 68 years.
Five months later in the 200m butterfly, he was the youngest man ever to set a swimming world record.
The boy from Baltimore hit Athens in 2004, equalling Mark Spitz's record of four golds won in single person events. He finished with eight medals in one Olympics, a feat only achieved by Russian gymnast Alexander Dityatin at Moscow in 1980.
FACTS & STATS
Born: 30 June 1985, Baltimore, Maryland, USA
Trains: Michigan, USA
Career highlights: eight medals at Athens Olympics (04)
Turned professional: aged 16
PATH TO THE PODIUM
2008 form: Good, very good. Following up his seven-gold haul in last year's world championships, he won his five individual events at the recent American trials, setting world records in the 200m individual medley and the 400m individual medley.
Rivals: American team-mate Ian Crocker has the potential to ruin the Phelps party as the two will go head-to-head in the 100m butterfly. Another American who may feel as though he was born at the wrong time is Ryan Lochte - he goes up against his friend in the 200m.
In peak training phases, Phelps will swim at least 80,000 metres a week
After narrowly losing to Phelps in the 400m individual medley in the trials, Lochte said: "I always feel like he's beatable. He's just a regular person."
How he could win: The question was how many he could win and can he better Spitz's seven gold medals? Australia's five-time Olympic swimming gold medallist Ian Thorpe said: "If there is any person on the planet who is capable, it is him. It's sad, but I don't think it will happen."
Spitz disagrees. "This is going to be history. He's going to do, as we say, a little schooling to the rest of the world."
What Phelps said about a possible eight golds: "I don't think anything is too high. The only way to think like that is if you put limits on yourself. The more you use your imagination, the faster you go. If you think about doing the unthinkable, you can. The sky is the limit."
What you say: "The Legend That Is Michael. I salute the GREATEST show on earth. Olympics absolutely RULE."
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Sporting highs: A fifth in the 200m butterfly at Sydney aged 15, six golds at Athens, and seven golds at last year's worlds, not to mention a whole bag of world records.
He's also probably quite satisfied after co-founding a program called "Swim with the Stars" which promotes the sport for all ages.
Sporting low: At Athens in 2004, Phelps had two chances to surpass Spitz's seven golds. In the 200m freestyle - dubbed the 'race of the century' - he had to settle for bronze behind Australian Ian Thorpe and Dutchman Pieter van den Hoogenband. It was another bronze in the 4x100m relay team.
AWAY FROM SWIMMING
Life before sport: The only thing before his swimming career was a very brief childhood. After taking up the sport aged seven there was no looking back. Former swimming coach Jon Urbanchek said: "When I first saw Michael in 1996, I looked at his stroke, I looked at his body type and said, 'This kid is going to be awesome'."
While Phelps's mum said: "He never sat still. He never shut up; he would never stop asking questions. He just wanted to go from one thing to another."
Hero worship: His reading material on his bookshelf would suggest where his worship lies - biographies on Lance Armstrong and former Green Bay Packers coach Vince Lombardi.
Most likely to: Be doing, in his words, "normal boring things" like looking after his pet bulldog Hermann, playing video games on his TV and lots of sleeping.
Least likely to: Be slipping into his armbands delighted just to be taking part in another Olympics. American team-mate Crocker says: "His motivation is that he just hates to lose. He's got a lot of biological advantages, plus that desire."
Did you know? In peak training phases, Phelps will swim at least 80,000 metres a week. That's nearly 50 miles. That includes two practices a day and sometimes three when he's training at altitude.