by Michael Rosenberg

You have to go outside his sport now, outside the Olympics. Phelps has become one of his generation's transcendent athletes — he defines swimming as much as swimming defines him. Only a few stars can say that, and their names are instantly recognizable.

Tiger.

Gretzky.

Pelé.

MJ.

Television executives know this all too well: Americans do not tune in to watch golf; they watch Tiger play golf. They are tuning in for greatness. Michael Jordan was far more popular in his prime than any athlete today, because Jordan gave people the image of athletic perfection. And now, even years after they retired, Wayne Gretzky and Pelé probably remain the most famous athletes in their sports, at least among Americans.

Gretzky's nickname — "The Great One" — says so much about this special group of performers. Phelps's appeal over the last week was not about swimming. It was about dominance. Americans are drawn to a phenomenon that scientists refer to as "supreme awesomeness." You might not know what a dolphin kick is, but you know that no man is supposed to be this good at anything.

This is why more than 10,000 Baltimore Ravens fans stuck around to watch a swimming race on the big screen. This is why Phelps has more 517,000 fans on Facebook and Aaron Piersol, arguably the best backstroker ever, has 4,000.

Is Phelps really 129 times as popular as Aaron Piersol?

Are you prepared to tell me he's not?

Phelps played "Risk" with his teammates to kill some of his down time, and veteran "Risk" players know that game served as a blueprint for his success: first you conquer Australia, then you take over the world.

Phelps came into these Games as the most hyped athlete in Olympic history. He then exceeded the hype. Every final was a novella, its own story within a story.

The first gold featured rare emotion on the medal stand. The second was a relay for the ages. The third, the 200 freestyle, was about sheer greatness — Phelps obliterated the field. The fourth was when he got water in his goggles and won blind. With the fifth, he broke the Olympic record for most medals by any athlete, in any sport. He led the sixth from start-to-finish. His seventh came down to a hundredths of a second, officially — and really, it was closer than that.

No. 8 made history. As teammate Aaron Piersol said "Spitzian achievement" is now outdated. This is a Phelpsian world, and the rest of them are just swimming in it.

Phelps said the lesson of his performance is that anything can happen if you believe in it. Yeah, OK. Tell that to the other swimmers.

Phelps is not just synonymous with swimming now. He is synonymous with greatness in swimming. That is a more elusive label, and it is the one that is stuck to him forever.

Think about it this way: Roger Federer might be the greatest tennis player ever. At his best, he certainly seems like the most complete player ever. I love watching the guy play. And more Americans watch tennis than watch swimming.

But in 20 years, who will be more famous in America? Phelps or Federer? I would bet on Phelps without hesitation. Federer, as great he is, can reasonably be called "unappreciated." Phelps is heavily appreciated, and that won't change unless somebody wins nine golds. There have been other iconic tennis players.

There is only one Michael Phelps.