She was known to be a "talking gorilla". Koko, the primate of the western lowland variety which had learnt sign languages numbering over 1,000 and made friendship with several celebrities while in captivity in the United States, died at the age of 46 earlier this week. She passed away in her sleep at the preserve of the Gorilla Foundation in California, the foundation's sources said.
Her death followed that of the world's oldest Sumatran Orangutan, named Puan, in a zoo in Australia at the age of 62.
Koko, who was born in San Francisco Zoo in 1971, was originally called "Hanabi-ko" which is the Japanese for "fireworks child", and was taught rudimentary sign language by a researcher called Dr Francine Patterson.
She reportedly knew around 2,000 verbal words in English and made it to the cover of the prestigious National Geographic and was also treated as the subject of various documentaries. She also knew how to play a recorder.
To give an example of the deceased gorilla's intelligence quotient, when the kitten adopted by Koko called "All Ball" died after getting hit by a car in 1984, Patterson had asked her about the incident and the ape had responded: "Cat, cry, have-sorry, Koko-love."
Even after the actor Robin Williams, with whom Koko had grown a special relationship in 2001, had passed away in 2014, Koko reportedly became "quiet and thoughtful" when learning about it.
Koko had turned into an icon by the virtue of her emotional and cognitive abilities and won millions of fans across the world.