In 1979, Koko and The Gorilla Foundation moved to the Santa Cruz Mountains where Ndume joined them as a fellow ambassador for their species.
Koko, the thoughtful gorilla who captivated the world through her ability to use sign language and revealed an empathetic side to great apes, has died.
Instructors taught her a version of American Sign Language and say she used it to convey thoughts and feelings.
The foundation said Koko's capacity for language and empathy opened the minds and hearts of millions. "She was beloved and wil be deeply missed". She eventually understand more than 1,000 signs and approximately 2,000 English words.
Koko featured in documentaries and appeared on the cover of National Geographic twice and started learning sign language when she was one year old.More news: Trump's migrant policy: First blowback, then about-face
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The first cover, in October of 1978, featured a photograph Koko had taken of herself in a mirror.
Videos featuring Koko and other kittens she has looked after have been viewed thousands of times worldwide.
She adopted and named pets, including a kitten she called All Ball.
"Koko touched the lives of millions as an ambassador for all gorillas and an icon for interspecies communication and empathy", the statement read.
The pair bonded in 2001 when Williams visited the foundation, and Koko insisted he tickle her and also wanted to try on his glasses.