For example, take Mary Lou Retton and Carly Patterson. Retton captured gold in 1984 and 24 years later remains a household name. Patterson also won the gold in women's gymnastics four years ago but hasn't had the same staying power.
In general, Americans have short memories. Will they remember the newly crowned gymnastics champion Nastia Liukin next year? It's a question that every champion and agent must consider in the afterglow of the Games.
Athletes and agents are well aware of the possibility of obscurity, and Phelps and his team are trying to make sponsorship decisions carefully. Surely it will be difficult for the eight-time gold medalist to completely fade away, but maximizing his star power in the long run is a different challenge.
For Phelps, appearances and endorsement possibilities have undoubtedly been flying from all directions. Phelps and his agent, Peter Carlisle at Octagon, are thinking carefully about their next steps to balance his clean-cut American image and cash in on one of the best sports marketing opportunities in history.
Carlisle told The Wall Street Journal last week that he expects Phelps' current annual earnings to at least double.
"What is the value of eight golds in Beijing before a prime-time audience in the U.S?" Carlisle told the newspaper. "I'd say $100 million over the course of his lifetime."
Phelps and Retton before him are two of a long series of American athletes who have taken advantage of their Olympic success. Many athletes, like decathlete Olympic champion Bruce Jenner, have made careers out of their Olympic fame.
American track star Carl Lewis has done the same. Twelve years after winning his last gold medal, Lewis came to Beijing to root for American athletes, and to promote McDonald's and their Champion Kids program.
At the fast food chain's promotional event, Lewis talked to children about what makes a champion and how one day he hoped to see the children racing on the track or winning in the Olympic pool.
"One day some of these kids are going to be Olympians and I will be excited to watch that," he told ABC News.
In the meantime, McDonald's is more than happy to watch Lewis in action.
Soon, Lewis will be joined by another Olympic champion, Phelps, and together the famous Olympians will continue mining more gold from their hard-won medals.