The most decorated Olympian in history, Phelps made his Olympic debut at the age of 15 at the 2000 Sydney Olympics.
Michael Phelps Olympic Games 2012 in London
As Michael Phelps adds to his extraordinary gold medal tally, we look at rival claims to be the Olympics' 'Greatest Of All Time' - and ask how you even judge.
USA's Michael Phelps laughs while posing with his gold medal on the podium of the Men's Freestyle Relay Final during the swimming event at the Rio 2016 Olympic Games at the Olympic Aquatics Stadium in Rio de Janeiro on August / AFP / GABRIEL BOUYS
Michael Phelps is the only athlete at Rio 2016 to wear an Olympics uniform that illuminates.
Rio Olympics Michael Phelps beats Ryan Lochte to win gold - BBC Sport
The BBC's David Willis visits the pool where swimmer Michael Phelps got his big start, and sees first-hand how fans in Baltimore celebrate his achievements.
Michael Phelps glowering at his rival Chad Le Clos at the 2016 Olympics -