Michael Phelps plays Lil Wayne's I'm Me to ready himself for action in the pool.

The greatest Olympian of all time, who has competed at three Games, is inspired by these lines:

Michael Phelps of the US prepares to swim in the men's 100m butterfly semi-finals at the National Aquatics Center during the Beijing 2008 Olympic Games August 15, 2008. [Agencies]

"I'm me, so who you? You're not me, you're not me and I know that ain't fair, but I don't care."

According to Today Morning Express his signature used to be worth just $25 but this has gone up to $500.

This is expected to rise even further, to $1,000 a signature, if he wins his eighth gold medal at the Games.