FILE - This combination of photos shows United States' Michael Phelps holding each of his eight gold medals after (top, left to right) the 400m individual medley, 4 x 100m freestyle relay, 200m freestyle, 200m butterfly, (bottom, left to right) 4 x 200m freestyle relay, 200m individual medley, 100m butterfly and the 4x100-meter medley relay at the Beijing 2008 Olympics in Beijing. Phelps retires with twice as many golds as any other Olympian, and his total of 22 medals is easily the best mark. (AP Photo, File)
Michael Phelps heads into retirement the only way imaginable — with an 18th Olympic gold medal.
Since his Olympic debut as a 15-year-old in Sydney a dozen years ago, Phelps has won twice as many golds as any other Olympian. His total of 22 medals is easily the best mark, too.
Phelps capped off a mind-boggling career with a victory in the 4x100-meter medley relay Saturday.
Here's a look back at Phelps' Olympic career in photos: