The 27-year-old bear was put down Tuesday, the New York Daily News reported. Zoo officials said he was examined because he had lost appetite and had problems chewing and veterinarians found a tumor near his thyroid.
Gus was born in the Toledo Zoo in Ohio and transferred to the Central Park Zoo in 1988.
In 1994, zookeepers noticed that Gus appeared to be swimming compulsively, The Gothamist said. Experts determined he was bored and an enrichment program was designed that included encouraging him to forage for food and giving him objects to manipulate.
Zookeepers also worried about his emotional well-being when his longtime companion at the zoo, Ida, died in 2011 at 25.
"Gus was an icon at the Central Park Zoo and a great source of joy for our visitors and staff," said Jim Breheny, executive vice president of the Wildlife Conservation Society, which runs the New York City zoos.