Michael Phelps is now one of the most famous swimmers of all time. But 16 years ago, he was a kid swimming in his first Olympics.
Phelps is notable not just for his swimming times but also for his history with the games. This is the fifth Olympics he's competed in. No other swimmer has competed in that many Olympic events.
The record-holding swimmer has also changed a lot personally throughout his career, from being a teenager to becoming a 31-year-old father.
Here are some photos that show his evolution, from his first Olympics to today.