Koko, the beloved gorilla that learned to communicate using sign language, has died

Koko and Penny Patterson. Koko has died aged 46. Photo / Gorilla Foundation

Koko, a beloved gorilla that learned to communicate with humans and then stole their hearts, has died.

The Gorilla Foundation said the 46-year-old celebrity ape - a western lowland gorilla - died in her sleep this week at the organisation's preserve in Northern California. The Gorilla Foundation, a nonprofit organisation that works to protect the species and their habitats, said in a statement that Koko will be remembered "as the primary ambassador for her endangered species".

Koko indicates 'eat' to Francine 'Penny' Patterson, who at the time was graduate student at Stanford and Koko's main instructor. Photo from 1975. Photo / Getty

"Koko touched the lives of millions as an ambassador for all gorillas and an icon for interspecies communication and empathy," the statement said. "She was beloved and will be deeply missed."

The gorilla was born at the San Francisco Zoo on Independence Day in 1971 and officially named Hanabi-ko, which means "fireworks child" in Japanese, although she was mostly known by her nickname, Koko, according to the Gorilla Foundation.

Koko napping with a doll in June, 2015. Photo / Gorilla Foundation / Ron Cohn

It was in San Francisco where the newborn gorilla met a budding animal psychologist, Francine "Penny" Patterson. By the next year, Patterson had started teaching Koko an adapted version of American Sign Language, which she called "Gorilla Sign Language," or GSL.

Video footage from that time shows Patterson playing games with the baby gorilla and teaching her how to sign.

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It grew into a decades-long friendship that revealed a deeper side of Koko and her ability to understand, although some experts questioned Patterson's methods and Koko's abilities. (As Slate noted four years ago: "In the past few decades there has been a spirited debate about whether apes are using language in the same way humans do.")

Koko also built relationships with Mister Rogers, Betty White and Robin Williams.

She loved baby dolls. And kittens.

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"Koko's capacity for language and empathy has opened the minds and hearts of millions," the Gorilla Foundation said in its statement. "She has been featured in multiple documentaries and appeared on the cover of National Geographic twice. The first cover, in October of 1978, featured a photograph Koko had taken of herself in a mirror. The second issue, in January of 1985, included the story of Koko and her kitten, All Ball. Following the article, the book Koko's Kitten was published and continues to be used in elementary schools worldwide.

"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."