LONDON (AP):He's won all 13 of his races, is regarded as one of the world's greatest racehorses, and has made Britain's most-acclaimed trainer feel young again during a battle with cancer.

In the space of two years, Frankel - the world's top-ranked thoroughbred - has left a huge imprint on racing. His dazzling career will come to an end this weekend in front of Queen Elizabeth II and 32,000 spectators at Ascot.

After tomorrow's Champion Stakes, where he is seeking to increase his career earnings to nearly £3 million (US$4.85 million), Frankel will settle down to a life of luxury as a stallion for his Saudi owners.

"It's for others to sum him up but we'll remember him with fantastic fondness as really the ultimate equine athlete," Teddy Grimthorpe, racing manager to Frankel's owner Khalid Abdullah, told The Associated Press. "I'm biased, but I think he's the best there has ever been."

inspiration and challenge

Frankel's breathtaking performances have touched the hearts of British audiences since his first win, as a 2-year-old, in August 2010.

And they have brought his trainer, Henry Cecil, back into the public consciousness in a way he could never have imagined.

Cecil was diagnosed with stomach cancer in 2006 and has looked frail in recent public appearances, his voice quiet and low and much of his hair gone.

Nurturing Frankel to the top has made him feel "20 years better".

"I am so lucky to have been allocated Frankel to train," Cecil said Thursday. "He has been an inspiration and challenge, which I really needed so badly. Through my illness, I feel that the help from my wife, Jane, and the determination to be there for Frankel has helped me so much to get through the season."

Cecil has been training horses for 43 years and regards Frankel not only as the best horse he has handled but the best he has ever seen.

Frankel, named after American Hall of Fame trainer Bobby Frankel, has arguably his toughest assignment ahead of him tomorrow as he aims for a 14th straight win.

Cirrus Des Aigles, the defending champion, and Nathaniel - two horses in the top five in the International Federation of Horseracing Authorities' world thoroughbred rankings - will be in the field of six gunning for the first prize of £737,230 (US$1.19 million).

And the going is forecast to be soft - the first time Frankel has run on heavy ground since his debut race, when he won by only half a length.

But bookmakers listed him as 1-6 favourite yesterday and even his rivals don't expect Frankel to slip up.

"Obviously, we're all going out to beat him, but he's unbeatable," said jockey William Buick, who will ride Nathaniel. "I think on Saturday he'll go out and do what he always does.

Frankel set the bar high when he romped to his first English classic victory, in the 2,000 Guineas at Newmarket in April 2011. At one stage, the colt was 15 lengths clear, sparking an outbreak of spontaneous applause from spectators, before crossing the line ahead by six lengths.

As a 4-year-old, he has been even more dominant, winning the Queen Anne Stakes at Royal Ascot by 11 lengths in June and the International Stakes at York by seven lengths in August. It was an unprecedented eighth straight European Group One win and lifted his rating with Timeform - a company that rates performances by horses - to 147, its highest ever mark.

Only Dancing Brave, winner of the 2,000 Guineas and Prix de l'Arc de Triomphe, has been rated higher by handicappers at the British Horseracing Authority.