In recent weeks, Ivan lost weight and his appetite and was battling a respiratory illness, Hayley Murphy, the zoo's director of veterinary services, said Tuesday morning in an emailed statement.
Because of his declining health, Ivan underwent a diagnostic assessment by zoo doctors on Monday, according to Keisha Hines, zoo spokeswoman.
But Ivan never regained consciousness following the use of general anesthesia, Hines said.
"General anesthesia carries a degree of risk in any veterinary procedure, but these risks are compounded in an individual of Ivan's advanced age and delicate condition," Murphy said. "We are heartbroken that this proved the case, and Ivan did not recover from the anesthesia."
Born in the wild in 1962 in what is now the Democratic Republic of Congo, Ivan had lived at Zoo Atlanta since 1994.
Ivan has no immediate survivors. A necropsy will be performed at the University of Georgia.
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