
U.S. swimmer Michael Phelps -- the most decorated Olympian of all time -- celebrates with his gold medal after the 4x200 freestyle on Tuesday, August 9. Phelps has won 21 gold medals so far in his career (25 medals in all), and he's looking to add more to his collection in Rio de Janeiro.

Phelps competes in the 100-meter butterfly during the Rio Games.

Phelps celebrates after winning the 200-meter butterfly in Rio. The victory avenged a loss at the 2008 Games in Beijing.

Phelps takes part in a qualifying race in Rio for the 200-meter individual medley.

Phelps shows off his gold medal from the 200-meter medley at the London Olympics. It was his 20th career medal.

Phelps celebrates in 2012 after becoming the most-decorated Olympic athlete in history. He had just won his 19th medal after the 4x200 freestyle.

Phelps competes in the 200-meter butterfly in London.

Phelps celebrates with teammates after winning the 4x100 freestyle in London.

Phelps looks on during the 4x100 freestyle in London.

Phelps climbs out of the pool in London after a shock fourth-place finish in the 400-meter medley.

Phelps is hugged by teammate Ryan Lochte in 2008 after winning the 200-meter medley in Beijing. Phelps won eight gold medals in Beijing -- the most-ever in one Olympics.

Phelps sets a world record in the 200-meter butterfly in Beijing.

Phelps shouts encouragement to teammates in the 4x200 freestyle in Beijing.

Phelps won six gold and two bronze medals in the 2004 Summer Games in Athens, Greece. Here, he holds a bronze from the 200-meter freestyle.

Phelps celebrates winning gold in the 400-meter medley in 2004. It was his first Olympic gold, and it came in a world-record time of 4:08.26.

Phelps smiles after winning the 200-meter butterfly during the U.S. Olympic Trials in 2004.