ATLANTA — Ivan, the geriatric gorilla, who lived half his life in a Tacoma, Wash., shopping mall before moving to Zoo Atlanta, passed away Monday night during a diagnostic exam.

The 50-year-old gorilla had been declining during the last few weeks, as digestive problems took away his appetite and arthritis made it hard for him to move around his outdoor enclosure.

Zoo Atlanta’s veterinarians had planned to conduct a complete medical workup on Aug. 27, but moved that date up to Monday as Ivan’s condition worsened. Over the weekend Ivan declined to leave his indoor sleeping area, according to deputy director Dwight Lawson.

A team of vets anesthetized Ivan around 4:30 EDT Monday afternoon to check for major problems. He moved into recovery about an hour later, but never woke from general anesthesia. “He basically died in his sleep,” said Dr. Hayley Murphy, director of veterinary services at the zoo.

While the final cause of death will be determined by a necropsy being conducted at the University of Georgia’s veterinary school, Ivan showed little evidence of cardiac disease, which is usually a major concern for older gorillas.

Collected from the wild around 1962, Ivan lived for 27 years in a glass and steel cage in a circus-themed shopping center, until mounting pressure convinced his owners to give him to Seattle’s Woodland Park Zoo.

Though in the care of Zoo Atlanta, Ivan remained the property of the Seattle zoo, and his remains may be shipped back to Washington, Lawson said.

Despite his solitary life, Ivan learned to live with other gorillas. He never sired any offspring, however, and for the past year has lived alone. “For me the best thing to remember,” said Dr. Murphy, “is that he died in peace.”

Murphy added one bright note to Tuesday’s somber news: Lulu, another gorilla in Zoo Atlanta’s collection, is pregnant.