Andre Ward: American two-weight world champion retires from boxing
Unified light-heavyweight world champion Andre Ward has retired, ending a career which delivered world titles across two weight divisions.
Ward, 33, held titles at super-middleweight but moved up a weight division and unified the WBA, IBF and WBO light-heavyweight belts in 2016.
In a statement he said his body could not "put up with the rigors" of boxing.
"If I cannot give my family, my team, and the fans everything I have, then I should no longer be fighting," he said.
'Top of a glorious mountain'
Earlier in the week Ward posted an image to social media showcasing titles he had earned during his career.
He last fought in June when he stopped Sergey Kovalev in a Las Vegas rematch to defend the titles he had won in a unification bout with the Russian seven months earlier.
Ward inflicted the only defeats of Kovalev's career and his perfect 32-fight record also boasts victories over names such as Carl Froch and Mikkel Kessler during time spent at super-middleweight.
"To the sport of boxing - I love you," wrote the 2004 Olympic gold medallist. "You've been by my side since I was 10 years old. You've taught me so much. You've humbled me. You've promoted me.
"As I walk away from the sport of boxing today, I leave at the top of your glorious mountain, which was always my vision and my dream. I did it. We did it."
After turning professional after his Olympic success in 2004, Ward took five years to land his first world title with a shock victory over Kessler.
That success arrived in the Super Six World Boxing Classic tournament, where Ward later beat Arthur Abraham and Froch to take the trophy and unify the WBC and WBA belts at super-middleweight.
'One of the best displays I've seen' - Analysis
BBC Sport boxing correspondent Mike Costello:
Ward's decision comes as a huge surprise and as with any such announcement in boxing will be greeted with scepticism.
He is ranked by many as the best pound-for-pound boxer in the world today and he is the last American male to win Olympic gold.
His win against Froch in 2011 was high amongst the best performances I have seen as a commentator at ringside.
'Congrats champ!' - Reaction to Ward's retirement
Former world featherweight champion Barry McGuigan: What an outstanding box/fighter, happy retirement Andre Ward Champ.
IBF welterweight champion Errol Spence: Hall of Famer, went out on top as the pound-for-pound king. Hope to be able to do the same someday. Salute bro.
Former two-weight world champion Paulie Malignaggi: Congrats Andre Ward on a Hall of Fame career! Honoured to have been ringside to see you work over the years. Enjoy the next chapter.
Former British super-middleweight champion Paul Smith Jr: Great career, great fella. Did it his way and retired on top. Never got the credit he deserved but beat them all. Congrats champ.