Lance Armstrong, who recovered from cancer to win the Tour de France a record seven times, announced his retirement yesterday, a month after his last race.
The 39-year-old American, who made a comeback to the sport two years ago, said he was quitting for good to spend more time with his family and working for his charities.
"I am announcing my retirement from professional cycling in order to devote myself full-time to my family, to the fight against cancer and to leading the foundation I established before I won my first Tour de France," he said.
Armstrong initially retired from cycling in 2005 but returned in '09, finishing third in the Tour in his first year back.
His final race was at the relatively low-key Tour Down Under in Australia last month.
Armstrong was diagnosed with testicular cancer in '96 but survived and returned to the bike and went on to become one of the most successful and controversial cyclists of all time.
He won the Tour de France for an unprecedented seven consecutive years, from '99 to 2005, before quitting at the top.
He made a comeback at the age of 37, saying he partly missed the thrill of competition but was driven by a greater cause, to help promote cancer awareness through his charity Livestrong.
Armstrong enjoyed mixed success but did not add to his record number of Tour de France wins.
He finished a third behind his team-mate Alberto Contador in 2009 then 23rd last year.
Armstrong said last year that January's Tour Down Under would be his last international race. He planned to compete in the US this year, including the Tour of California, before quitting for good yesterday.
Meanwhile, Contador was back on his bike at the Tour of the Algarve yesterday, just one day after escaping a doping ban .