Koko, the gorilla who mastered sign language, has died.
The Gorilla Foundation said the 46-year-old western lowland gorilla died in her sleep at the foundation's preserve in Northern California's Santa Cruz Mountains on Tuesday.
Koko was born at the San Francisco Zoo, and Francine Patterson began teaching the gorilla sign language as part of a Stanford University project in 1974.
The foundation said Koko's capacity for language and empathy opened the minds and hearts of millions.
Koko appeared in many documentaries and twice in National Geographic magazine. The gorilla's 1978 cover featured a photo that the animal had taken of herself in a mirror.