Keo the chimp was moved into a public display this week at the zoo's Regenstein Center for African Apes after spending most of the last four years in a habitat out of public view, the Chicago-Sun Times reported.
Keo's 50th birthday is June 26.
Zoo workers say the 5-foot tall, 117-pound chimp is "a very congenial guy" and is in healthy condition with only slight arthritis in one finger.
Keo has had two mates and sired 11 offspring, but now has undergone a vasectomy, even though the chip "still has it in him," researcher Steve Ross said.
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