The Gorilla Foundation has confirmed that Koko the gorilla passed away in her sleep aged 46 on Wednesday. The statement said: '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.’Koko had a long life - the average lifespan of a gorilla is 35-40 years. But Koko was truly remarkable in many ways.Sign languageKoko first became famous in 1978 when she featured on the cover of National Geographic magazine, taking a picture of herself in the mirror.Francine 'Penny' Patterson, Koko's instructor and caregiver, began instructing her in a modified version of American Sign Language (ASL) from the age of 1. According to Patterson, Koko was able to use over 1000 signs. She could also understand 2000 words of spoken English. She didn't just repeat signs, Koko was able to convey her emotions through sign language too - when her beloved pet kitten All Ball died, she cried and signed 'Sad, bad, sad' and 'Frown, cry, frown, sad'. Celebrity friendsKoko had a lot of celebrity visitors, including Betty White and Leonardo diCaprio. In 2001, she struck up a particular friendship with the actor Robin Williams - who described meeting her as 'unforgettable'. When Koko was told of his death in 2014, Koko signed the word 'cry' and looked 'quiet and thoughtful'.Dr. Penny Patterson said that 'Koko and Robin's encounter is a supreme example of how humans and gorillas can overcome interspecies boundaries and express the highest form of empathy - embracing differences.'Koko certainly leaves an important legacy behind, having taught us a lot about gorillas' capacity for both language and empathy.