Koko was also said to have understood some 2,000 words of spoken English.

Koko, a western lowland gorilla said to have mastered American Sign Language, has died aged 46, the California institute which studied her said on Thursday.

“The Gorilla Foundation is sad to announce the passing of our beloved Koko,” the research centre said in a statement, adding she passed away in her sleep.

Koko was among a handful of primates who could communicate using sign language; others included Washoe, a female chimpanzee in Washington state, and Chantek, a male orangutan in Atlanta.

Her keepers said she understood some spoken English, too.

While some scientists questioned the sign language claim, the “talking” lowland gorilla nevertheless became an ambassador for her species, which is threatened by logging and poaching in their native habitats in central Africa.

Koko’s capacity for language and empathy opened the minds and hearts of millions of people, the foundation said.

“[She] 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,” it said.

Watch the video … https://t.co/8CjbommeQF — Gorilla Foundation (@kokotweets) April 19, 2018

‘Fascinated by Koko’

Koko was born Hanabi-ko (Japanese for “Fireworks Child”) on July 4, 1971 at the San Francisco Zoo.

Dr Francine “Penny” Patterson began working with Koko the following year and taught her sign language, the foundation said.

The gorilla was featured in many documentaries and appeared on the cover of National Geographic magazine twice, once – in October 1978 – in a photograph Koko had taken of herself in a mirror.

She was very maternal towards kittens, and had several throughout her lifetime. Her “tenderness” showed people how loving a gorilla can be, the foundation said.

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

She painted objects in her environment but also expressions of her thoughts and emotions. She used signed language to name her paintings, and she was said to have understood some 2,000 words of spoken English.

In 1998, Koko took to the Internet in what was billed as the first “interspecies” chat, relaying comments such as “I like drinks” via a human interpreter to tens of thousands of online participants.

The foundation says it will honour Koko’s legacy with a sign language application featuring Koko for the benefit of gorillas and children, as well as other projects.