He died in his sleep while at home in Dallas, US, on Thursday (local time), sports author Ron Palenski confirmed this morning.
Sir Peter would have turned 81 years old on Tuesday.
“Peter had had heart problems in recent years but his wife Miki said she wanted people to know he was living his life and not bed-ridden,” Palenski wrote on Facebook.
“Peter fell asleep and died around noon while waiting to go shopping with Miki. They had talked about playing table tennis that night.
Palenski shared several photos of Sir Peter over the years “to remind people of what a great athelete he was”.
“He was also a great man.”
Sir Peter burst on to the world athletic scene in 1960 at the Rome Olympics, racing the 800 metres and stunning the world by beating the record holder Belgium’s Roger Moens.
Four years later at the Tokyo Olympics, he won both the 800 metres and the 1500 metres.
In just four years, the super strong athlete, built more like a rugby midfield back than a track star, notched up eight world records and won the title of the greatest Iron Man in the history of middle distance running.
In the mid-70s, now 37 years old, Sir Peter started his life anew in the United States. Always seeking privacy, he found it at a California University in studies into sports medicines.
One of his early tests on stamina and strength was on New Zealand’s John Walker, the first athlete to clock up a sub-3:50 mile.
Over the years Sir Peter returned regularly from the United States with his wife Miki to visit his mother.
She lived in the house built by Sir Peter and his brother when the family moved to Pukekohe in south Auckland.
One of the highlights of his visit home in 1990 was being given the honour of carrying the royal baton at the opening of the 14th Commonwealth Games at Mt Smart Stadium.
He was knighted in 2009.