Michael Phelps celebrates after becoming the most decorated Olympic athlete in history winning his 19th medal in the men's 4 x 200-meter freestyle relay final at the London Games on July 31, 2012. 
Phelps competes in the men's 200m butterfly final on Day 4 of the London 2012 Olympic Games. Winning a silver medal, his 18th, Phelps matches the record for most decorated Olympian alongside USSR gymnast Larysa Latynina. 
Phelps celebrates with the rest of the swimming team from the U.S. (Adrian Nathan (L), Ryan Lochte (2nd L) and Cullen Jones) after winning the silver medal in men's 4 x 100m Freestyle Relay final. 
U.S. swimmer Michael Phelps did end up qualifying for eight events but dropped 200-meter freestyle. Here, he looks on during the men's 4 x 100-meter freestyle relay final on Day 2 of the London Olympics. 
Phelps previously said before the London games that he would not compete in eight events again (like Beijing four years prior). Here, a disappointed Phelps climbs out of the pool after a shock fourth place in the final of the men's 400-meter individual medley on Day 1 of the London 2012 Olympic Games. 
Fellow teammate Ryan Lochte hugs Phelps who seems in shock or just exhausted after win in the men's 200-meter individual medley final race in Beijing. Phelps won eight gold medals during the 2008 Summer Games. 
Not just an individual winner, but also a team player. Phelps shouts encouragement to Peter Vanderkaay (with fellow teammates Ricky Berens, Ryan Lochte) in the men's 4 x 200-meter freestyle relay final on Day 5 of the Beijing 2008 Olympic Games. The team won the race and set a new world record of 6:58.56. 
Phelps competes in the men's 400-meter individual medley final during the XII FINA World Championships in Melbourne, Australia. Not only does he win, he also sets a new world record. 
Gold medalist Ian Thorpe of Australia, silver medalist Pieter Van Den Hoogenband of the Netherlands (L) and bronze medalist Michael Phelps of USA (R) pose with their medals after the medal ceremony for the men's swimming 200 freestyle event in 2004. In total, Phelps won six gold and two bronze medals in Athens. 
Phelps of the United States celebrates winning gold in the men's swimming 400-meter individual medley final on August 14, 2004. 
Team USA's Michael Phelps pictured during a training session prior to the Athens 2004 Summer Olympic Games at the Olympic Sports Complex Aquatic Centre. Just days later, Phelps would win the 400-meter individual medley, with a world record time of 4:08.26 and his first Olympic gold medal. 
Michael Phelps smiles after winning the 200-meter butterfly final during the U.S. Swimming Olympic Team Trials on July 10, 2004 at the Charter All Digital Aquatic Center in Long Beach, California. 
Michael Phelps of the U.S. swims his way to win the men's 200-meter individual medley final at the Pan Pacific Swimming Championships in Yokohama, Japan on 29 August 2002. Phelps won the final smashing his own record set the previous year with the championship record time of 1 minute 50.70 seconds. 
- Michael Phelps swam one event in his first Olympics, placed fifth
- At age 15, though, people saw his potential to be great swimmer
- Three Olympics later he has most medals of all time, most golds
- He raised the popularity of the sport in America through record-setting performances
(CNN) -- He was only a kid, a 15-year-old with braces, when he first dove into the Olympic spotlight.
He didn't win any medal at the Sydney Olympics, but he gave fans a tiny glimpse of what was to come when he swam the last 50 meters of the 200-meter butterfly faster than anyone else in the pool. He moved from eighth to fifth and moved from side note to talking point just like that.
His teammate Tom Malchow told reporters at those 2000 Games, "He's a true competitor, and he's going to be one of the greats."
Malchow likely meant swimming great. But did anyone expect the long, lean teenager from Baltimore to grow up to be possibly the greatest Olympian in history?
On Tuesday, Phelps won his 19th Olympic medal, more than many countries have ever won.
"It's a combination of everything," he told reporters last week on how he became the biggest name in swimming. "You have to have a great work ethic. Have a strong mind, be motivated. There are so many things that come into it.
"I have a decent package so I can't complain."
The United States has been a world power in swimming since the days of Johnny Weissmuller, but Phelps has elevated its status like no other American competitor.
NBC once broadcast the world championships live, a rarity for the sport, because Phelps was so popular. He was the first swimmer to win Sports Illustrated's Sportsman of the Year.
After every Summer Olympics the number of swimmers increases, but when Phelps won eight gold medals in an electrifying eight days in Beijing in 2008, it grew exponentially more than previous post-Olympic years, according to a 2009 article in the Orlando Sentinel.
Fresh off his record-setting Beijing performance, in an offseason where he was more concerned about tricking out his new apartment than training, he told Sports Illustrated he wasn't worried about the future even though he was out of shape and had put on some pounds.
"When I have to turn the switch back on, I know I can. All I have to do is put my mind to something and that's it, it's done," he said. It took a few years, but after some controversy he became motivated again.
He was banned from competition for three months in 2009 after a tabloid newspaper ran a photo of him appearing to inhale from a marijuana pipe. He almost retired, but decided the London Games would be his sendoff from the sport he began as a wispy child in Baltimore.
Phelps, who began swimming to emulate his sisters at age 7, set individual world records 29 times, and still owns records in six events. In the three competitve races he has left he won't be besting those times, now that he's almost a swimming old man (and due to slower swimsuits).
He wraps up a career as the most decorated Olympian ever, perhaps the greatest ever. Some commentators will argue the cases of track and field's Carl Lewis, who missed an Olympics due to a U.S. boycott, or distance runner Paavo Nurmi, who won 12 medals. Some might argue for Bjorn Daehlie, the Norwegian cross-country skier. And there's gymnast Larisa Latynina, whose 18 medals are now second all time.
It's a class for which it doesn't take to call roll.
