"He is in the top tier of athletics and now he's going to get his tryout as a personality," said John Sweeney, director of sports communication at the University of North Carolina at Chapel Hill's School of Journalism and Mass Communication. "And Tiger Woods sure passed, but Mark Spitz didn't. And there are plenty of people who they try to develop the whole persona around and two years later it's gone."
Phelps has won 14 gold medals, the most of any Olympian ever. Eight of those were at the Beijing Olympics, which end Sunday. His achievements at this Olympics broke American swimmer Spitz's record of seven golds at the 1972 Olympics in Munich for most won in at one time.
Phelps already has top endorsements -- from companies like Visa, Speedo, Omega, Hilton, and AT&T. And he's certainly got a big fan base -- or Phans as they call themselves. On the online networking site Facebook, more than 795,000 people have officially declared themselves fans of Phelps. That's a boost of more than 120,000 just on Monday.
That's a lot of people -- with a lot of buying power.
His agents at Octagon know it. Peter Carlisle, who leads the Olympic and action sports division there, told The Wall Street Journal in a story Monday he expects Phelps' current earnings of between $3 million and $5 million a year should at least double, or more, because of his performance in Beijing.
"What is the value of eight golds in Beijing before a prime-time audience in the U.S?" Carlisle told the paper. "I'd say $100 million over the course of his lifetime."
Visa, which has had a long-standing relationship with Phelps, was quick to put out new ads celebrating his big feats -- when he won his tenth career gold medal, which made him the winningest Olympian ever, and later, when he won his eighth gold at Beijing.
Phelps already has been one of the focal points of Visa's 'Go World' campaign, which uses rich sepia tones and slow, focused shots to tell stories of athletes and the Olympics.
As soon as he hit the two milestones, Visa aired the new ads at the very next commercial break. The company also took out print ads over the weekend and on Monday.
In the television spots, actor Morgan Freeman narrates as pictures of Phelps swimming stream past:
"One gold medal is amazing. Two is ... well ... incredible. Three? Practically unbelievable. But eight? Eight gold medals? That's ... that's well ... well, we're going to need some new adjectives for whatever that is. Congratulations, Michael," said one ad.
Kevin Burke, head of Visa's global consumer marketing, says the company is proud to have Phelps affiliated with the brand and wanted to recognize his achievements. Visa declined to say what it was paying Phelps, and it's not clear yet where the pairing will go.
"We continue to evaluate post-Beijing activities that will allow us to reinforce our relationship with Michael," Burke said.
New companies are coming after Phelps, too. Carlisle told the Journal he's getting up to 50 pitches a day.
The beverage PureSport is about to launch its first national advertising campaign with Phelps as a spokesman. Phelps, who is sponsored by the sports performance brand, also drinks it, along with his teammates, said its maker, Human Performance Labs. Chief Executive Michael Humphrey said the company, not even a year old, plans a big campaign with Phelps and gymnast Nastia Liukin, who also uses PureSport.
"It's huge. It's the opportunity that no startup generally gets," Humphrey said from Beijing. "With opportunity obviously there's a lot of responsibility for us to take advantage of it properly and do it in a way that not only benefits the company but also benefits Michael."
He said the company has a "substantial" multi-year deal with Phelps but declined to give specifics.
Pizza Hut, part of Yum Brands Inc., is giving Phelps and his teammates on the men's and women's U.S. swim team free pizza and pasta for a year. The company didn't say if it would do any advertisements with the team but said it would be willing to join in public appearances.
Another one of his sponsors, Kellogg Co., is also looking to bank on the wins.
"We are currently evaluating opportunities to build upon this excitement; however, a final determination about our future plans has not yet been made," the company said in a statement.