Koko, a gorilla who became famous for her ability to communicate through sign language, has died in her sleep at the age of 46, according to The Gorilla Foundation.
"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 organization said in a statement.
The western lowland gorilla died Tuesday at the foundation's preserve in California's Santa Cruz Mountains.
Born at the San Francisco Zoo in 1971 on the Fourth of July, Koko was named "Hanabi-ko," which means "fireworks child" in Japanese.
Animal psychologist Francine "Penny" Patterson began to teach Koko sign language a year later while she was a graduate student. Patterson, along with biologist Ronald Cohn, eventually would go on to help establish The Gorilla Foundation in 1986.
"Koko's capacity for language and empathy has opened the minds and hearts of millions," the foundation said in its statement.
Koko's extraordinary communication skills landed her two covers on "National Geographic." For the first one in 1978, she took her own picture through a mirror. Koko appeared in her second cover in 1985 with All Ball, an abandoned kitten she received as a birthday present.
Koko gained some famous friends throughout her life, including comedian Robin Williams.
In a 2001 video that captured a meeting between the two, Koko is seen joking around with Williams, at one point pulling his glasses off his face and trying them on her own. Toward the end of their meeting, Koko kissed Williams' hand, then pulled him in for a big hug.
Williams described the "mind-altering experience" of communicating with Koko as "awesome and unforgettable.
Koko also became friends with Mr. Rogers, whom she taught how to say "love" in sign language.
Thousands of people expressed condolences and their memories of growing up with media stories about Koko on the Gorilla Foundation'sFacebook page.
"Legit bawling like a baby right now. This news just breaks my heart," wrote Jess Cameron in the comments. "From an early age I was fascinated with Koko and she taught me so much about love, kindness, respect for animals, and our planet."