One of two male western lowland gorillas at the Cleveland Metroparks Zoo died Friday, zoo officials said in a Facebook post.
The 32-year-old gorilla, Bebac, was diagnosed with heart disease in 2008. Heart disease is common in gorillas who live in captivity, according to the BBC.
In an interview with ABC News, Zoo Executive Director Chris Kuhar called Bebac "one of the zoo's iconic animals."
Dozens posted tributes and photos of Bebac on the zoo's Facebook page.
Bebac and 29-year-old gorilla Mokolo both came to Cleveland from Chicago's Lincoln Park Zoo in 1994.
Bebac's health began deteriorating about a month ago and the zoo's medical staff struggled to treat him. The average life expectancy for gorillas living in captivity is about 30 years, according to ABC.
"It's been hard on the staff," Kuhar told ABC. "It's like losing a family member."
Mokolo, the surviving male western lowland gorilla, was also diagnosed with a heart condition in 2008. In 2011, the zoo reported that both he and Bebac's health had improved after they were placed on high-fiber diets.
"Through the care provided by our skilled team of gorilla specialists, we were able to manage his [Bebac's] condition and improve his quality of life for several years," zoo officials said on Facebook.
Zoo staffers said Mokolo appears to be affected by Bebac's death and seems agitated.
It's still too soon to say where the zoo will find another companion for Mokolo.
This past year hasn't been a good time for gorillas in captivity.
Last May, Harambe, a 17-year-old western lowland gorilla, was shot after a child fell into his habitat at the Cincinnati Zoo.
The Associated Press contributed to this report.