Legendary stallion A.P. Indy has died aged 31 at his home at Lane's End Farm in Kentucky.

Often referred to as a breed shaper, A.P. Indy was the United States Horse of the Year in 1992 and went on to sire some of the best horses in North America.

The son of triple crown winner Seattle Slew was retired from stud duties in 2011, and lived a comfortable life at the farm where he was born in Versailles, Kentucky.

"A.P. Indy passed away peacefully in his stall at the Lane's End stallion complex, the barn he called home for 27 years," a statement from Lane's End said.

"Champion A.P. Indy's list of accomplishments range far and wide as his legacy continues to be carried through the outstanding performances of his sons and daughters across the globe.

"He was the most important and popular member of the Lane's End team and we are deeply sorry to all who loved him as much as we did."

Lane's End said A.P. Indy had been in relatively good health and his death came from the infirmities of old age.

A.P. Indy was the highest-priced yearling of his year at $2.9 million and won the 1992 Belmont Stakes and Breeders' Cup Classic after missing the Kentucky Derby through injury.

He went on to be North America's leading sire in 2003 and 2006 with champions Mineshaft and Bernardini among his progeny.

His son Pulpit has in turn produced champion California Chrome and leading sire Tapit.