OLYMPICSMichael Phelps through the yearsMichael Phelps and teammates celebrate on the podium after winning the men's 4x100-meter medley.Rob Schumacher, USA TODAY SportsMichael Phelps celebrates with teammates after they won the men's 4x100-meter medley relay.Rob Schumacher, USA TODAY SportsMichael Phelps swam the butterfly leg during the men's 4x100 medley relay.Erich Schlegel, USA TODAY SportsMichael Phelps , Laszlo Cseh (HUN) and Chad le Clos (RSA) hold up their silver medals after the men's 100-meter butterfly.Rob Schumacher, USA TODAY SportsMichael Phelps reacts after finishing in a three-way tie for second in the men's 100-meter butterfly.Erich Schlegel, USA TODAY SportsMichael Phelps swims during the men's 100-meter butterfly final.Robert Hanashiro, USA TODAY SportsMichael Phelps holds up four fingers, for his fourth gold of the Rio Games, after winning the men's 200-meter individual medley.Rob Schumacher, USA TODAY SportsMichael Phelps reacts after winning the men's 200-meter individual medley.Erich Schlegel, USA TODAY SportsMichael Phelps races Ryan Lochte during the men's 200-meter individual medley.Erich Schlegel, USA TODAY SportsWith the U.S. men's win in the 4x200-meter freestyle relay, Michael Phelps earned his 21st career gold medal.Kevin Jairaj, USA TODAY SportsMichael Phelps celebrates after the U.S. men's 4x200m freestyle relay captured the gold medal.Jason Getz, USA TODAY SportsMichael Phelps swam the anchor leg of the men's 4x200 freestyle relay.Kevin Jairaj, USA TODAY SportsMichael Phelps celebrates with his gold medal on the podium after the men's 200-meter butterfly. It was the 20th gold of Phelps' career.Rob Schumacher, USA TODAY SportsMichael Phelps celebrates after winning the men's 200-meter butterfly.Rob Schumacher, USA TODAY SportsMichael Phelps swims during the evening men's 200 butterfly.Kevin Jairaj, USA TODAY SportsMichael Phelps kisses his gold medal after the U.S. men's 4x100m freestyle relay team captured gold.Rob Schumacher, USA TODAY SportsMichael Phelps and Caeleb Dressel celebrate after winning the men's 4x100m freestyle relay final.Rob Schumacher, USA TODAY SportsMichael Phelps swims during the men's 4x100m freestyle relay final.Rob Schumacher, USA TODAY SportsMichael Phelps leads the U.S. team into the stadium during the opening ceremony of the Rio Games.Rob Schumacher, USA TODAY SportsMichael Phelps (USA) swims prior to the start of the Rio Games.Rob Schumacher, USA TODAY SportsMichael Phelps celebrates at the medal ceremony after winning the men's 100m butterfly final at the U.S. Olympic swimming team trials.Rob Schumacher, USA TODAY SportsMichael Phelps swims during the men's 100 meter butterfly semifinal at the U.S. Olympic swimming team trials.Erich Schlegel, USA TODAY SportsMichael Phelps swims laps during a practice session for the Arena Pro Swim Series at Skyline Aquatic Center on April 15.Rob Schumacher, USA TODAY SportsOlympic gold medalist Michael Phelps puts on his goggles for a practice session at the Arena Pro Swim Series on at Skyline Aquatic Center on April 15.Rob Schumacher, USA TODAY SportsMichael Phelps during the men's 100m butterfly race at the 2014 USA Swimming Grand Prix Series.Joe Camporeale, USA TODAY SportsMichael Phelps and Ryan Lochte after the men's 100m butterfly race at the 2014 USA Swimming Grand Prix Series.Joe Camporeale, USA TODAY SportsMichael Phelps swims in the winning the gold medal during the men's 4x100m medley relay final during the London 2012 Olympic Games.Rob Schumacher, USA TODAYAt the USA Swimming Olympic Team Trials Michael Phelps wins the Men's 200 Meter Butterfly Finals.Rob Schumacher USA TODAY SportsMichael Phelps wears a huge smile after winning the 200M Individual Medley final on day six of the US Olympic Team Trials in 2004 for swimming at the Long Beach Swim Stadium in Long Beach.Eileen Blass USA TODAY SportsMichael Phelps holds a U.S. flag as he walks around the pool with his teammates following the medal ceremony for the men's 4x200 freestyle relay at the National Aquatics Center in Beijng.Eileen Blass USA TODAY SportsMichael Phelps hugs teammate Erik Vendt in 2004.Eileen Blass USA TODAY SportsMichael Phelps and Takashi Yamamoto of Japan show off their gold and silver medals they won in the men's 200 meter butterfly finals at the 2004 Olympics.Eileen Blass USA TODAY SportsMichael Phelps of the USA leaves the starting block in heat 9 of the men's 100m butterfly preliminaries Thursday at the National Aquatics Center in Beijing.Eileen Blass USA TODAY SportsMichael Phelps (gold) right, and Ryan Lochte (bronze), at the medal ceremony for the men's 200m individual medley Friday at the National Aquatics Center in Beijing.Eileen Blass USA TODAY SportsMichael Phelps wins the Men?s 200M Individual Medley Final at the National Aquatics Center in Beijing.Daniel J. Powers USA TODAY SportsMichael Phelps, the most decorated Olympian in history, appears on the December issue of Golf Digest in 2012.Walter Iooss Jr Golf DigestMichael Phelps prepares for the Men?s 200M Individual Medley Final at the National Aquatics Center in Beijing.Daniel J. Powers USA TODAY SportsMichael Phelps shows off his gold medal.Daniel J. Powers USA TODAY SportsMichael Phelps after a training seassion in 2004.Eileen Blass USA TODAY SportsMichael Phelps stretches before swimming in the Men's 200 Meter Freestyle Prelims in the USA Swimming Trials.Rob Schumacher USA TODAY SportsMichael Phelps enjoys short track speedskating in Vancouver.Robert Deutsch USA TODAY SportsMichael Phelps off the blocks on his way to winning the 200M Individual Medley final on day six of the US Olympic Team Trials for in 2004.Eileen Blass USA TODAY SportsMichael Phelps pulls a weighted sled across a dock on Baltimore Harbor during his workout prior to the 2012 Olympics.H. Darr Beiser USA TODAY SportsEncore Olympian Michael Phelps "Media Day" at Under Armour. Michael Phelps works with trainer Keenan Robinson during his dry-land workout.H. Darr Beiser USA TODAY SportsMichael Phelps pauses during swimming practice.H. Darr Beiser USA TODAY SportsIn 2008, in China, USA'S Michael Phelps in the water during his leg of the men's 4x100 meter medley relay finals ahead of Australia with the USA men's team taking the gold medal in world record time of 3:29.34 . Photo by Jack Gruber, USA TODAY Staff ORG XMIT: JG 34514 swim day 9 8/17/2008 (Via MerlinFTP Drop)Jack Gruber USA TODAY SportsOlympic Gold Medalist Michael Phelps looks ahead to the London 2012 games.Kevin Moloney For USA TODAYMichael Phelps swims in the Men's 200 Meter IM Prelims, during the USA Swimming Trials.Rob Schumacher USA TODAY SportsFrom left Michael Phelps , Nathan Adrian , and Cullen Jones react after finishing second in the men's 4x100m freestyle finals during the London 2012 Olympic Games.Kyle Terada USA TODAY SportsDebbie Phelps the mother of Michael Phelps reacts after catching a bouquet of flowers after the men's 4x200m freestyle relay finals during the London 2012 Olympic Games.Kirby Lee USA TODAY SportsMichael Phelps walks on the sidelines before the NFL football AFC Championship football game between the New England Patriots and the Baltimore Ravens in Foxborough, Mass.,Stephan Savoia APORG XMIT: USPW-92164 Jul 25, 2012; Michael Phelps answers questions from the media during a press conference at Speedo Club at Forman's Fish Island.Rob Schumacher USA TODAY SportsAt the 2008 Beijing Summer Olympics Michael Phelps , left, yells with Garrett Weber-Gale, right, as the USA team came from behind thanks to USA anchor swimmer Jason Lezak, in water, to win the gold during the men's 4x100 meter freestyle relay finals at the National Aquatic Center at the Beijing Olympic games.Jack Gruber USA TODAY SportsMichael Phelps (center) waves to the crowd as the 2012 USA Olympic Swimming Team is introduced.Rob Schumacher USA TODAY SportsAt the USA Swimming Olympic Team Trials in 2012 Michael Phelps swims in the Men's 400 Meter IM Prelims.Rob Schumacher USA TODAY SportsUSA swimmer Ryan Lochte (top black cap) looks at Michael Phelps as he laughs during practice four days before the 2012 London Olympics.Rob Schumacher USA TODAY SportsMichael Phelps (USA) wears a pair of headphones before competing in the men's 4x100m freestyle finals during the London 2012 Olympic Games.Kyle Terada USA TODAY SportsMichael Phelps is photographed underwater following practice at the Meadowbrook Aquatic & Fitness Center in Baltimore.Eileen Blass, USA TODAY SportsUSA swimmers Michael Phelps (right), , Brendan Hansen (center) and Matthew Grevers (left) celebrate as Nathan Adrian swims the anchor leg, winning the gold medal in the men's 4x100m medley relay final during the London 2012 Olympic Games.Rob Schumacher USA TODAY SportsAn 18-year-old Michael Phelps adjusts his goggles.Eileen Blass USA TODAY SportsMichael Phelps walks to the start of the Mens 400M Individual Medley Wednesday evening at the Long Beach Swim Stadium in Long Beach, CA. He won the race with a time of 4:08.41, a new world record.Eileen Blass USA TODAY SportsMichael Phelps speaks to the media following his final race as an Olympian. Or what was thought to be his final race.Michael Madrid USA TODAY SportsMichael Phelps reacts after a tee shot on the fourth hole during The Annexus Pro-Am at TPC Scottsdale.Rick Scuteri USA TODAY SportsUSA swimmer Michael Phelps watches the preseason game between the Golden State Warriors and the Los Angeles Lakers.Danny La Danny La USA TODAY SportsUSA swimmer Michael Phelps celebrates after winning the gold medal in the men's 4x100m medley relay final during the London 2012 Olympic Games.Rob Schumacher USA TODAY SportsUSA swimmers Matthew Grevers, Brendan Hansen, Michael Phelps and Nathan Adrian celebrate on the podium after winning the gold medal in the men's 4x100m medley relay final during the London 2012 Olympic Games.Rob Schumacher USA TODAYMichael Phelps, left, joins Michelle Obama, center, and Justin Tuck, right, and local area kids for lunch at a SUBWAY store in 2013.Nick Wass Invision For SUBWAYPhelps pleaded guilty to driving under the influence and received 18 months of supervised probation. He was arrested Sept. 30, 2014, and he went to court Dec. 19.Patrick Semansky, APMichael Phelps swims the 200-meter individual medley during the AT&T Winter National Championships at the Weyerhaeuser King County Aquatic Center.Getty ImagesMichael Phelps waves to the crowd after winning the 200-meter butterfly finals at the AT&T Winter National Championships at the Weyerhaeuser King County Aquatic Center.Getty Images