Tributes have been flooding in for Ian Thorpe after he announced his retirement from the sport at the tender age of 24 today.

Political figures, former swimmers, coaches and officials all joined in acknowledging the achievements of a man who won 11 world titles, five Olympic gold medals and set 13 individual long-course world records in a glittering career.

The tribute that means most in swimming terms comes from Doug Frost, under whose guidance Thorpe won eight world titles and broke 11 world records over 200m and 400m freestyle, and two over 800m.

Their relationship ended in 2002 when Thorpe left Frost for assistant Tracey Menzies. Now coaching at the Australian Institute of Sport, Frost congratulated Thorpe on a wonderful career.

"I am very pleased for Ian that he has made a decision on his future. I think it has been obvious to many people that he has struggled for motivation for quite some time now. While Ian and I parted ways in 2002, I have always keenly followed his progress and am very proud of everything he has achieved in his swimming career and his life.

"I've been in touch with Ian this afternoon to express this to him and to reiterate to him how incredible his swimming achievements have been. I'd like to publicly thank Ian for the great memories he has given me and I wish him the best with whatever he decides to pursue next; whatever he does, I have no doubt he will do it successfully."

Frost first met Thorpe as an eight-year-old when he arrived at Padstow swimming pool. Almost immediately Frost recognised talent in Thorpe, and six years later he was in the national swim team on the path to an incredible career.

"By the age of 11 he was displaying incredible talent," recalled Frost. "At 13 he basically won everything on offer at national age championships and it was then for the first time that I had no doubts this young man would one day be an Olympic and World Champion. A great many people questioned me at the time as to why I was investing so much time in this young kid. I had no such doubts. I could see the exceptional natural talent he had and his dedication and commitment to doing everything in his power to be the best.

"I had no doubt he would achieve every goal he set himself for."

Frost said his greatest Thorpe moment was his 2000 Sydney Olympic performance when the then 18-year-old won three gold medals and a silver despite a bronchial infection. It was an incredible performance that amazes me to this day," he said.

Aussie legend Dawn Fraser went a little over the top, saying that Thorpe deserved to remembered as the best of all time. "He rates as the greatest swimmer in the world as far as freestyle swimming is concerned," Fraser told Australian TV.

Tell that to Mark Spitz and Don Schollander. They broke more records and they won more medals but that's memory for you.

"I was hoping he may have gone on to Beijing to do the three events in a row and I guess in a way I'm sad. But that's selfish of me because he's made that decision for himself, he doesn't want to put himself under any more pressure, and I say 'thank you very much for what you've done'."

Shane Gould, who won three gold medals at the 1972 Munich Olympics before retiring at 16, said Thorpe would be missed but she understood his decision to retire prematurely.

"It's going to be sad because he was an inspirational performer and just so theatrical and just a glory to watch in his black suit and his rippling muscles and his focused attention," Gould told ABC.

"He could probably swim faster and I probably could have swum faster and won more medals but look, swimming's just swimming, there's a whole life out there.

"He's really saying ... I achieved all that I wanted to achieve and I felt that there was more in life to experience and do. There comes a time when that curiosity and that instinct is triggered."

The President of the Australian Olympic Committee, John Coates, said Thorpe's achievements would stand the test of time. "In fifty years from now Australians will still marvel at the feats of Ian Thorpe," Coates said in a statement. He has been a great champion, a great inspiration for young Australians and a fine ambassador for his country."

Australia's Prime Minister John Howard described him as a remarkable swimmer and "a good bloke", adding to reporters on a tour of Vietnam: "His retirement is an enormous loss to Australian swimming but it's tough, he started early, all swimmers do. Millions of Australians will remember his wonderful individual performances."

Thorpe was a hero and legend at home but was embraced like one of their own in Japan, where in 2001 at Fukuoka he won a record six world titles.

"It's really too bad. I didn't believe it when I heard it," said Koji Ueno, the director of Japan's national swim team, on news of Thorpe's retirement. "That we can't see him swim anymore is really a shame. Especially at the world championships next March, I'd looked forward to some good competition."