Koko, the gorilla whose apparent aptitude for sign language endeared her to fans around the world, died in her sleep on Tuesday morning in California, according to the Gorilla Foundation, which oversaw her care. She was 46.

Koko became an instant celebrity in her youth thanks to an early facility with American Sign Language. That fame was bolstered over the years as Koko, a western lowland gorilla, charmed entertainers like Fred Rogers and Robin Williams as well as their audiences.

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

By the age of 4, Koko had developed a vocabulary of more than 170 words and showed an ability to use language creatively, Penny Patterson, her longtime caretaker and trainer, told The New York Times in 1975.