Veteran American trainer D Wayne Lukas has been forced to retire due to ill health.
Lukas, 89, has reportedly turned down an aggressive treatment plan having been suffering from an infection and is due to leave hospital and return home to his family.
His long-serving assistant, Englishman Sebastian 'Bas' Nicholl will take over the running of his stable.
"Wayne is one of the greatest competitors and most important figures in thoroughbred racing history," said Mike Anderson, president of Churchill Downs said on Churchill Downs' official website.
"He transcended the sport of horse racing and took the industry to new levels. The lasting impact of his character and wisdom – from his acute horsemanship to his unmatched attention to detail – will be truly missed. The enormity of this news is immense, and our prayers are with his family and friends around the world during this difficult time."
Lukas, who was inducted into the Hall of Fame in 1999, has won the Kentucky Derby four times, among his 15 Triple Crown race wins, and has 20 victories at the Breeders' Cup, a record matched only by Aidan O’Brien.
Lukas trained his last winner on 12 June at Churchill Downs when Tour Player was successful. His first thoroughbred success came in October 1977.
Nicholl, a former tank commander in the British Army, said: "Wayne built a legacy that will never be matched. Every decision I make, every horse I saddle, I’ll hear his voice in the back of my mind. This isn’t about filling his shoes – no one can – it’s about honouring everything that he’s built."
Some of Lukas' best horses included Thunder Gulch, owned by Michael Tabor, Winning Colors and Tabasco Cat.
