Koko, the western lowland gorilla who was taught sign language by Dr. Francine Patterson in the early 1970s, died this week in her sleep at the age of 46, the Gorilla Foundation said Thursday.
Koko famously appeared on the 1978 cover of National Geographic in a photo she took of herself in a mirror. Koko "revealed the depth and strength of a gorilla's emotional life," NPR writes, mourning her adopted kitten, Ball, when it was hit by a car in 1984. "Cat, cry, have-sorry, Koko-love," Koko had signed to Patterson in response to the question "What happened to Ball?" She reportedly knew some 1,000 signs, and 2,000 words of spoken English, the New York Post reports.
The Gorilla Foundation wrote that Koko's "impact has been profound and what she has taught us about the emotional capacity of gorillas and their cognitive abilities will continue to shape the world." Learn more about Koko in the documentary below. Jeva Lange