New Zealand running great Peter Snell, a triple Olympic gold medallist, has died at the age of 80, sports historian Ron Palenski said on Saturday.
Palenski, a close friend, said Snell's wife Miki had phoned him from their home in Dallas to tell him of the death.
The couple were preparing to go shopping when "Peter nodded off, as is not unusual for him. But he didn't wake up," Palenski said.
Snell, a protege of famed coach Arthur Lydiard, was the most dominant middle-distance runner of his era.
He won gold in the only three Olympic events he contested -- the 800 metres at Rome in 1960 and the 800m and 1500m in Tokyo four years later - set world records for the mile and 800m and also won dual gold at the 1962 Commonwealth Games in Perth.
He was the first male athlete to win the 800m-1500m double at an Olympics since 1920, a feat that has not been achieved by any male since.
Shell was voted New Zealand's "Sports Champion of the Century" and was one of 24 inaugural members of the International Association of Athletics Federations Hall Of Fame.
"He is probably the greatest athlete New Zealand has had," Palenski told AFP.
Snell had suffered heart problems for a few years and was unable to attend a recent dinner in Monaco for mile world record holders.
"I even tried to go against my heart failure doctor's advice and showed up at the airport for my flight," he said in a message to the galaxy of mile stars who attended.
"I felt that it was too risky to board an eight-hour flight given how poorly I was feeling at the time."
After a relatively short athletics career, Snell retired in 1965 and moved to the United States where he gained a Bachelor of Science in human performance from the University of California, Davis, and then a PhD in exercise physiology from Washington State University.