"The greatest Olympic athlete of all time"
Phelps retires with twice as many goldmedals as any other Olympian, and with a total of 22 medals achieved over the last three Olympics.
Phelps swam into retirement the best way possible - with an 18th gold medal. Reaffirming the lead with his signature butterfly stroke, the one seen in his Olympic debut as a 15-year-old in Sydney, he crowned his career with a victory in the 4x100-meter medley relay.
"I did it," Phelps said. "Through the ups and down of my career, I've been able to do everything I've wanted to accomplish."