But it's not just attitude - it is anatomy. His coaches spotted it when he was still a teenager: a body custom made for swimming glory, CBS News correspondent Barry Petersen reports.
"Once every 10 to 15 years one sort of rises up like a phoenix who is born to do what they do," said former swimming champion Diana Nyad. "He's built and born for swimming."
As he was growing up, his torso extended beyond what's normal. While he's 6 feet 4 inches in height, he has the upper body of a man 6 feet 8 inches. That gives him extra upper-body strength. But Phelps also has the legs of a man who's only 5 feet 10 inches, which provides him with more efficient kicking.
His arms stretched out of proportion to his body: to 6 feet 7 inches. It means more arm muscles and bigger hands for pulling through the water.
And his feet grew to a huge size 14.
Swimmers use their ankles like fish use fins for propulsion. His ankles do it better.
"The ankle flexibility is what pushes water backwards so that you go forward," said swimming coach and former Olympic medalist Clay Evans. "It's that simple, and he has great ankle flexibility. Just incredible and big feet so it's a big flipper with the capability of moving in the right direction."
After each swim, his ear is pricked to measure lactic acid, which causes fatigue. For reasons no one knows, he produces less than most other athletes, so he recovers faster.
Mark Spitz set the record for most gold medals in one Olympics at seven.
So in Beijing, everyone is focused on Phelps breaking that record by winning eight golds by the time he is done. Everyone … except Michael Phelps.
"I'm not even thinking about it. I've got eight races, and I've got to take them one by one," Phelps said.
Low key - you bet. He likes to sleep in and plays cards for fun.
He gobbles food, 10,000 to 12,000 calories a day. That's four to five times what an average person should eat.
That's energy he burns in the pool, in Beijing. Competing in heats and finals, he will have swum enough laps to equal a runner having to finish eight 26-mile marathons.
And can you imagine swimming against him? At these Olympics his competitors have mostly seen his back - the guy who is always in front and always pulling away.