Betsy, the oldest western lowland gorilla at Melbourne Zoo, died yesterday aged 50.
A central figure in the zoo's breeding program for the endangered species, Betsy had been losing weight for several months and began refusing to eat or drink in recent days.
She suffered from cardiac disease and in 2003 had a kidney removed after a life-threatening infection.
Zoos Victoria's director of life sciences, Matt Vincent, said while her death was not unexpected, due to her age, it was a significant loss.
Betsy was euthanased yesterday.
"Everyone who works at Melbourne Zoo will share in the sadness of this loss, but Betsy will always be remembered as having played a major role in the gorilla breeding program," Mr Vincent said.
Betsy arrived from Taronga Zoo in 1980, and later produced two offspring - Buzandi, who is now in a breeding program in Germany, and Bambuti, who is in a breeding program in Britain's Channel Islands with Mzuri, Australia's first gorilla baby.
Western lowland gorillas are under extreme threat in the African wild. Much of the tropical forest primates' habitat is being cleared, while they are also killed for their meat, which is sold in cities and towns.