Koko, the gorilla who mastered sign language, has died.
The Gorilla Foundation says the 46-year-old western lowland gorilla died in its sleep at the foundation's preserve in California's Sana Cruz mountains on Tuesday.
Koko was born at the San Francisco Zoo, and Dr. Francine Patterson began teaching the gorilla sign language that became part of a Stanford University project in 1974.
The foundation says Koko's capacity for language and empathy opened the minds and hearts of millions. (NBC4)