Bebac was diagnosed with heart disease nearly nine years ago. Fellow gorilla Mokolo is now all alone.
One of two western lowland gorillas at the zoo in Cleveland, Ohio, has died, the zoo said at the weekend.
Bebac died on Friday at the age of 32. He was diagnosed with heart disease in 2008.
"Through the care provided by our skilled team of gorilla specialists, we were able to manage his condition and improve his quality of life for several years. This is an extremely difficult loss for everyone connected with Cleveland Metroparks Zoo," the zoo commented on its Facebook page.
Bebac's fellow gorilla at the zoo, Mokolo, was also diagnosed with heart disease in 2008. The zoo tried to manage the gorillas' health by changing their diet and encouraging foraging.
Gorillas can live 50 years or more in captivity or in the wild. Colo, 60, a female at the zoo in Columbus, Ohio, is the oldest gorilla in the United States.
Several US zoos have western lowland gorillas. One gorilla was shot and killed last year at the nearby Cincinnati zoo after a child fell into the cage. The shooting sparked widespread public criticism.
There are an estimated 100,000 western lowland gorillas in the wild in central Africa, according to the International Gorilla Conservation Program. Western lowland gorillas are classified as threatened and their populations are in decline due to habitat destruction, disease and hunting. They are the gorillas most commonly seen in zoos.
There are an estimated 5,000 eastern lowland gorillas in the Democratic Republic of Congo (DRC), which are vulnerable to extinction. Mountain gorillas, confined to two small populations in Uganda, Democratic Republic of Congo and Rwanda, are one of the most endangered species on the planet. There are no captive mountain gorillas.