According to the Gorilla Foundation, which monitored her care, Koko, the gorilla whose apparent mastery of sign language won her admirers from all over the world, passed away in her sleep on Tuesday morning in California. She was 46.

Koko’s early proficiency in American Sign Language helped her become an instant star when she was young. As Koko, a western lowland gorilla, won over artists like Fred Rogers and Robin Williams as well as their fans throughout the years, his renown grew.

The Gorilla Foundation said in a statement that “Koko touched the lives of millions as an advocate for all gorillas and an emblem for interspecies communication and empathy.” She was cherished and is going to be greatly missed.

According to Penny Patterson, Koko’s lifelong trainer and carer, The New York Times reported in 1975 that by the time she was 4 years old, Koko had amassed a vocabulary of more than 170 words and had the capacity to utilize language imaginatively.

At the time, Dr. Patterson observed that “she occasionally makes up new words [signs] which are incredibly suitable and she is able to tie familiar phrases together in creative and meaningful patterns.” “Koko also plays word games and has a sense of humor.”

Due to her fluency in several languages, Koko appeared on the 1978 and 1985 covers of National Geographic and was the focus of numerous documentaries. According to the charity, Koko had amassed a vocabulary of more than 2,000 words by the time of her passing.

However, immediately after Koko became well-known, some scientists started to doubt the depth of her talents, claiming that she was only reacting to cues or that Dr. Patterson and others had exaggerated her talent by interpreting her acts in a way that suited their own agendas. Through the years, the discussion persisted, but it had little impact on waning public interest in Koko.

She gave the impression that she was happy, frustrated, and heartbroken while in public. She had always been kind to animals and was especially kind with cats. The well-known children’s book “Koko’s Kitty” was inspired by her love with a kitten named All Ball.

Her connections with well-known people, such as Mr. Rogers, whose television program “Mister Rogers’ Neighborhood” included Koko in one episode in 1998, further contributed to her notoriety. According to Margy Whitmer, one of the show’s longstanding producers, that appearance was among the most memorable ones.

With Mr. Rogers, Koko instantly felt at ease, playing with his sweater and telling him she liked him.

This year, Ms. Whitmer told The Times, “He simply welcomed Koko and was extremely calm with her and really exhibited no fear.”

Three years later, Koko met Robin Williams and clicked with the actor and comedian right away. Mr. Williams praised the incident in interviews and even made light of it during a stand-up performance. He passed away in 2014, and Koko was apparently devastated.

According to the Gorilla Foundation, Koko was born on July 4, 1971, in the San Francisco Zoo as Hanabi-ko, which is Japanese for “Fireworks Child.” The next year, she started working with Dr. Patterson, who was at that time a Stanford University psychology PhD candidate.

The Gorilla Foundation was established by Dr. Patterson in 1979, and it was later relocated to the Santa Cruz Mountains.

According to the Smithsonian’s National Zoo and Conservation Biology Institute, wild gorillas normally live for 30 to 40 years, although those kept in human care can survive into their 50s. Koko is one of an extremely rare breed of lowland gorillas found in the western hemisphere.