Phelps was born in Baltimore, Maryland.
Phelps' rapid improvement culminated when he qualified for the 2000 Summer Olympics at the age of 15, as became the youngest male (since Ralph Flanagan in 1932) to make a U.S. Olympic swim team in 68 years.
At the World Championship Trials for the 2001 World Aquatics Championships, on March 30, Phelps broke the world record in the 200-meter butterfly to become, at 15 years and 9 months, the youngest male ever to set a world record in swimming.
At Nationals, Phelps won the 200-meter freestyle, 200-meter backstroke, and the 100-meter butterfly. He became the first American swimmer to win three different races in three different strokes at a national championship.
In his first event, the 400-meter individual medley, Phelps won his first Olympic gold medal in the world record time of 4:08.26.
On August 17, Phelps won his eighth gold medal in the 4×100-meter medley relay, breaking Mark Spitz's record of seven gold medals won in a single Olympic Games, which had stood since 1972.
On July 28, 2012, Phelps placed eighth in the morning prelims for the 400-meter individual medley. Phelps, the two-time defending Olympic champion, won his heat in 4 minutes, 13.33 seconds with a time that was well off his world record of 4:03.84 set four years ago in Beijing, when Phelps won a record eight gold medals.
After the 2012 Olympics, Phelps retired from swimming, stating: "I'm done. I'm finished. I'm retired. I'm done. No more," and that "I just wanted to be done with swimming and didn't want anything to do with the sport anymore."
In April 2014, Phelps announced he would come out of retirement, and would enter an event later that month.
Phelps was chosen to be the American flag bearer at the opening ceremony, which was the first Olympic opening ceremony that he would attend.
On August 13, in the 4 × 100-meter medley relay, Phelps ended his career with another gold medal, his 23rd at the Olympics and his 28th medal overall.