Koko - a gorilla who became famous after learning sign language - has died in her sleep aged 46.
The animal, who made several celebrity friends during her life - including late comic Robin Williams - 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 next year, famously teaching her sign language. Dr. Patterson and Dr. Ronald Cohn moved Koko and the project to Stanford in 1974 and went on to establish The Gorilla Foundation.
According to The Gorilla Foundation: "Koko's capacity for language and empathy has opened the minds and hearts of millions. She has been featured in multiple documentaries and appeared on the cover of National Geographic twice.
"The first cover, in October of 1978, featured a photograph Koko had taken of herself in a mirror. The second issue, in January of 1985, included the story of Koko and her kitten, All Ball. Following the article, the book Koko's Kitten was published and continues to be used in elementary schools worldwide.
"Her impact has been profound and what she has taught us about the emotional capacity of gorillas and their cognitive abilities will continue to shape the world."
Koko the gorilla has died aged 46
Life in captivity
But vegan activists have spoken out about how living in captivity is harmful for animals. According to People for the Ethical Treatment of Animals [PETA]: "Gorillas enjoy highly social multifaceted relationships.
"Their lives revolve around their families. These keenly intelligent primates are quiet and peaceful. They grieve and have been documented holding wakes for lost loved ones.
"In captivity, virtually everything that gives their lives meaning is lost. Captive gorillas can become profoundly depressed."
The charity adds that 'The Gorilla Foundation was cited numerous times by the U.S. Department of Agriculture [USDA] for its deteriorating facilities and improper veterinary care for Koko'.
"In one alarming instance in 2014, she was described as not feeling well and was said to be unwilling to use her legs and to have reduced function in one of her arms but wasn’t examined by a veterinarian," says PETA, adding that the foundation received an official warning after the USDA found cleaning violations during six separate inspections.
The charity says: "To pay real homage to Koko, to do something in her memory that helps others kept in captivity, please think of her before sharing captive-animal memes on social media, and recall the sacrifices that the animals in them make in order for us to have a quick laugh or a light-hearted moment."