Sir Henry Cecil has died at the age of 70, said a statement posted on the Newmarket trainer's official website on Tuesday.
Responsible for 25 British Classic winners and crowned champion trainer 10 times, Cecil was also the leading handler by some way at Royal Ascot with a record 75 successes.
Knighted by the Queen in 2011, his later years saw him battle cancer but were illuminated by the great Frankel, officially the best horse in the world and unbeaten in 14 starts before retirement.
A statement posted on his website read: "It is with great sadness that Warren Place Stables confirms the passing of Sir Henry Cecil earlier this morning. Following communication with the British Horseracing Authority, a temporary licence will be allocated to Lady Cecil. No further update is anticipated this afternoon."
Told of the news during a press conference on racing's finances, Paul Bittar, chief executive of the British Horseracing Authority, said: "He's been one of the great characters in British racing for a long time, he had endless numbers of wonderful horses. It's tragically sad but what a great way to end a career, with one of the best horses any of us will ever see."
From an aristocratic background, Cecil first took out a training licence in 1969. He had his first British Classic win with Bolkonski in the 1975 renewal of the 2,000 Guineas at Newmarket, following up in the same race a year later with Wollow. Both horses were ridden by Frankie Dettori's father, Gianfranco.
Cecil excelled with fillies, and trained six 1,000 Guineas winners and eight Oaks victors, his last Epsom heroine being Light Shift in 2007. Four Derby winners - Slip Anchor, Reference Point, Commander In Chief and Oath - adorn his record, as do four St Leger triumphs.
Among his Leger winners was Oh So Sharp, who completed the fillies' Triple Crown of 1,000 Guineas, Oaks and Leger under Steve Cauthen, with whom Cecil enjoyed a spectacular association.
But for all the great horses to pass through his care, the best was saved until last as Frankel demolished everything put in his path. He retired to stud with an unbeaten 14-race record and was officially recognised as the greatest horse on the planet.
Cecil dominated Royal Ascot, which opens next Tuesday, like no other and the racecourse were quick to pay their respects.
Johnny Weatherby, Her Majesty The Queen's representative, said in a statement: "Obviously it is very sad to hear of the loss of Sir Henry Cecil this morning. He has been an intrinsic part of racing and Royal Ascot for the whole of his career. No one had more success at the meeting and his 75 winners are a long way clear of anybody else. Our thoughts are with his family at this moment and they will be throughout the whole of next week."
Newmarket Racecourse paid its own tribute to Cecil, who saddled no less than nine Guineas winners at the track during his career.
A statement read: "Everyone at Newmarket Racecourses is hugely saddened to hear the news that Sir Henry has passed away and our thoughts are very much with Lady Cecil and all of the family. He was a much-loved gentleman of our sport and his winners were always hugely well received at both the Rowley Mile and the July Course.
"In total, he had no less than nine 2,000 and 1,000 Guineas winners - more than any other trainer from the modern era. These successes, along with the many others he had at the highest level, will ensure he is remembered as one of the greats of his profession.
"Those of us at Newmarket Racecourses were lucky enough to regularly come into contact with Sir Henry and his kindness and willingness to help were greatly appreciated by us all. Only earlier this spring, he attended a meeting to offer his thoughts and advice regarding our race programme.
"We, like so many others, will miss him very much and will never forget just how much he contributed to the sport of racing, not least here at Newmarket Racecourses."
American rider Steve Cauthen enjoyed six memorable and highly successful years as stable jockey, including many Classic triumphs.
"It's a great loss to the sport and to everybody who knew him. he was such a great guy - different, special, a genius," he said.
"We had six great years together. The first year we had an amazing run when Slip Anchor won the Derby and Oh So Sharp won the Triple Crown for fillies. There were many others - Old Vic who won the French and Irish Derby, Reference Point, Indian Skimmer - there were so many of them.
"He had a great sense of humour. He was a super intelligent guy and really knew how to place his horses. He tried to have fun. The atmosphere during most of the time I was up at Warren Place was just fantastic.
"It was all due to him. It was a team effort but everyone looked to him. He was the one making decisions about where to run the horses. The way he trained was great and the way he placed them was fantastic. He was a special trainer.
"He went through a rough patch but he came back. To have a horse like Frankel and finish off his career when he wasn't in great health was incredible. He did a perfect job in making Frankel the horse he was."
Cecil, who had been battling stomach cancer for a long time, married his one-time secretary Jane McKeown in 2008.
He is survived by two children from his first marriage, Katie and Noel, and son Jake from his second marriage.
