The western lowland silverback was found dead by his "heartbroken" care team at Zoo Atlanta in Georgia, US, on Tuesday morning.

Ozzie's cause of death is unknown, but he is said to have lost his appetite since last week and was being provided with supportive care to encourage him to eat and drink.

But over the last 24 hours he had been treated for facial swelling, weakness and an inability to eat or drink, the zoo said.

Raymond B King, the zoo's president and chief executive, said: "This is a devastating loss for Zoo Atlanta. While we knew this time would come someday, that inevitability does nothing to stem the deep sadness we feel at losing a legend.

"Ozzie's life's contributions are indelible, in the generations of individuals he leaves behind in the gorilla population and in the world's body of knowledge in the care of his species.

"Our thoughts are with his care team, who have lost a part of their lives and a part of their hearts."

Last year, Ozzie was one of 13 gorillas at Zoo Atlanta who tested positive for COVID-19.

Officials said they believed the apes contracted it from a fully vaccinated zoo worker who was wearing protective equipment. The worker was asymptomatic.

The zoo said it would release the results of Ozzie's post-mortem after it is completed by the University of Georgia's veterinary college.

Ozzie was the only surviving member of the original generation of gorillas who arrived at Zoo Atlanta with the opening of its Ford African Rain Forest in 1988.

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In 2009, he made zoological history when he became the first gorilla in the world to participate in a voluntary blood pressure reading at the age of 48.

Gorillas are considered geriatric after the age of around 40.

Ozzie is survived by daughter Kuchi, sons Kekla, Stadi, and Charlie, granddaughter Lulu, great-granddaughter Andi, and great-grandson Floyd, all of whom live at Zoo Atlanta.

He also has other children, grandchildren, and great-grandchildren living at other accredited zoos in the US and Canada.