Sir Henry Cecil has died at the age of 70, said a statement posted on the Newmarket trainer's official website.
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 www.sirhenrycecil.com 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."
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 2000 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 1000 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 1000 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, 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.
