Koko, the gorilla who captivated imaginations with her ability to use sign language to communicate with humans, died in her sleep Tuesday morning. “The Gorilla Foundation is sad to announce the passing of our beloved Koko,” the organization said in a press release. Born July 4, 1971, Koko—named Hanabiko, which is Japanese for “fireworks child,” a nod to her birthday—was a western lowland gorilla who was chosen as an infant to work on a language-research project with psychologist Penny Patterson at the San Francisco Zoo. Koko became an icon, shooting her own portrait for a National Geographic cover in 1978, becoming pals with actor Robin Williams, and even having an adorable kitten, All Ball. The Gorilla Foundation said it would honor her legacy by continuing work on wildlife conservation, growing an ape sanctuary in Maui, and creating a sign-language app.