Michael Phelps with the gold medal he won in the 100m butterfly at the Olympic Games in Athens. On his head, he is wearing a crown of laurel leaves, like the ones awarded to winners at the ancient Olympic Games ©Getty Daniel Berehulak

Michael Phelps at the start of a race at the Olympic Games in Athens ©Getty Daniel Berehulak

Swim suit worn by Michael Phelps at the 2004 Olympic Games in Athens ©IOC / Donated by athlete

Michael Phelps - Beijing

Michael Phelps of United States, Chad Guy Bertrand le Clos of South Africa and Laszlo Cseh of Hungary celebrate winning silver in the Men's 100m Butterfly Final on the Rio 2016 Olympic Games at the Olympic Aquatics Stadium on August 12, 2016 in Rio de Janeiro, Brazil.

Michael Phelps of the United States competes in the Men's 200m Individual Medley Final on Day 6 of the Rio 2016 Olympic Games at the Olympic Aquatics Stadium on August 11, 2016 in Rio de Janeiro, Brazil.

Michael Phelps of the United States competes in the Men's 200m Individual Medley Final on Day 6 of the Rio 2016 Olympic Games at the Olympic Aquatics Stadium on August 11, 2016 in Rio de Janeiro, Brazil.

Michael Phelps of the United States competes in the Men's 200m Individual Medley Final on Day 6 of the Rio 2016 Olympic Games at the Olympic Aquatics Stadium on August 11, 2016 in Rio de Janeiro, Brazil.

Michael Phelps of the United States and Ryan Lochte of the United States compete in the Men's 200m Individual Medley Final on Day 6 of the Rio 2016 Olympic Games at the Olympic Aquatics Stadium on August 11, 2016 in Rio de Janeiro, Brazil.

Deborah Phelps (R), mother of Michael Phelps, and partner Nicole Johnson (C) with their son Boomer celebrate gold in the Final of the Men's 4 x 100m Freestyle Relay on Day 2 of the Rio 2016 Olympic Games at the Olympic Aquatics Stadium on 7th August, 2016 in Rio de Janeiro, Brazil.