Koko, the female western lowland gorilla known for having learned sign language, has died at the age of 46.
Announcing her passing today, the Gorilla Foundation said: "Koko touched the lives of millions as an ambassador for all gorillas and an icon for interspecies communication and empathy.
"She was beloved and will be deeply missed."
The famous gorilla died in her sleep yesterday morning, leaving behind an incredible legacy.
Known for mastering sign language thanks to Dr. Francine 'Penny' Patterson, Koko was born in 1971 at the San Francisco Zoo.
In 1974, Patterson and Dr Ronald Cohn took their project with Koko to Stanford, setting up The Gorilla Foundation - expanding the project to include a second western lowland gorilla called Michael.
Things then moved to the Santa Cruz Mountains in 1979, where another gorilla called Ndume joined the project.
Koko was even featured on the cover of National Geographic twice - once in October 1978, which was a photo Koko had taken of herself in a mirror, and then again in January in 1985, which covered the story of Koko and her kitten All Ball.
Koko, the gorilla known for sign language, has passed away at the age of 46. Here she is on the cover of the 1985 National Geographic. #RIPKoko pic.twitter.com/U95wNsGdWy
- Nat Geo Channel (@NatGeoChannel) June 21, 2018
The foundation's statement continued: "Her 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."
Saying that Koko's amazing capacity for language and empathy 'opened the minds and hearts of millions', the foundation added: "The foundation will continue to honor Koko's legacy and advance our mission with ongoing projects including conservation efforts in Africa, the great ape sanctuary on Maui, and a sign language application featuring Koko for the benefit of both gorillas and children."
Koko once met Robin Williams in a now-famous encounter. On hearing the news of his death a few years ago, the gorilla was said to be close to tears.
Recalling what happened when she was told of Williams' passing, the Gorilla Foundation said: "On Monday, Aug. 11, the day news broke of Williams' passing, Koko and Penny and Ron (Drs. Patterson and Cohn) were together when phone calls started coming in about the sad event.
"After the first call, Koko came to Dr. Patterson with an inquiring look on her face. Dr. Patterson explained that 'we have lost a dear friend, Robin Williams'. Koko was quiet and looked very thoughtful.
"More phone calls about the news came in, and Koko overheard one from a former colleague who had worked with Williams while he filmed a public service announcement for The Gorilla Foundation in 2003.
"The colleague's voice broke at the end of the conversation. About a half an hour later, Koko signed to Penny: 'CRY LIP' (LIP is Koko's sign for woman).
"At the end of the day, Koko became very somber, with her head bowed and her lip quivering."