Michael Phelps, the 19-year-old swimmer who won six gold and two bronze medals at the Athens Summer Games, has inked his first post-Olympic endorsement deal. Phelps can be seen listening to music on his headphones before a competition and, appropriately, signed with a maker of MP3 digital music players.

Matsunichi, a virtually unknown company looking to expand in Asia and Europe and enter the U.S. market, locked in Phelps to a four-year deal as chief spokesperson. The deal will include commercials and public appearances around the world.

Details of the endorsement deal haven't been released but ad pros say Phelps will bring in about $4 million over the next four years. If that prediction is true, that would make the deal the largest an Olympic athlete has ever signed.