Justin Gatlin, Athens 2004 Olympic sprint champion, retired from sprinting at the age of 40.
The four-time track and field world champion, who was twice banned for doping, explained this in an Instagram post to his "beloved career".
Gatlin wrote Thursday: "I loved you.
You have brought me tears of sadness and happiness and taught lessons I will never forget.”
Gatlin had won Olympic gold over 100 meters in 2004, in 2005 in Helsinki and in 2017 in London he also secured the world title over the short sprint distance.
He also won the 200m World Championships (2005) and the USA sprint relay (2019).
Prior to the Tokyo Olympics, Gatlin suffered a hamstring injury at the US Trials in Eugene and missed qualifying.
Gatlin was still a junior when he first committed a doping offense: in 2001 he was busted with a positive test for amphetamines, only having to sit out a year because the substance was part of a drug he had been taking for ADHD since childhood.
In 2006 he was banned for eight years - he was doped with testosterone, later his ban was reduced to four years.
For years, Gatlin was a competitor to superstar and world record holder Usain Bolt.
After his return in 2010, however, he only took silver behind the Jamaican at the World Championships in Moscow (2013) and Beijing (2015).
Bolt was also too strong for Gatlin at the games in London 2012 (bronze) and Rio 2016 (silver).
Only in London 2017 did he inflict a rare defeat on Bolt.