New chapter
Beckham placed eighth on the Forbes list of highest-earning athletes last year, raking in $46 million, most of which came from endorsements.
The Beckham brand is a family affair, with his wife Victoria matching his celebrity after swapping pop for fashion design, and one of their sons recently modelling for Burberry.
Beckham's commercial deals draw both on his looks and his reputation as a family man.
That versatility enables him to pose as an underwear model for fashion group H&M and act as an ambassador for supermarket group Sainsbury's efforts to get more children doing sport.
"For David Beckham, it extends the life of his brand further. Just when you thought it was over, it carries on going," said Chadwick.
Beckham has had a long relationship with Adidas. He signed his first contract with the German sportswear company in 1996 when he was beginning to make a name for himself at Manchester United.
"As a long term sponsor of David Beckham we would like to congratulate him on his move to Paris Saint-Germain. We look forward to continuing working with him in the future," Adidas said in a statement.
Beckham's critics argue that he is more style than substance, his image helping him to win more publicity than his footballing abilities now merit.
However, those who have worked with him have praised his professionalism and desire for the game.
AC Milan director Umberto Gandini welcomed the move to the French capital. "Great player and great person, he deserves it. Bonne chance!" he said on the Twitter social media site.
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