Koko was born in 1971 at the San Francisco Zoo.More news: First lady Melania Trump visits US-Mexico border amid separation crisis
"Betty met Koko in 2004 and became best friends nearly immediately", says the description of their meeting on The Gorilla Foundation's website. Her "tenderness" showed people how loving a gorilla can be, the foundation said. Following the article, the book Kokos Kitten was published and continues to be used in elementary schools worldwide.
"She was beloved and will be deeply missed", it said.
Koko met a slew of celebrities over the years, like Betty White, Leonardo DiCaprio and the late Robin Williams - who shared hugs and laughs with the gorilla during their 2001 encounter. Williams, who died in 2014, was filmed interacting with Koko in what he described as an "unforgettable" experience.
She adopted and named pets, including a kitten she called All Ball.More news: Chinese paper says Trump administration has 'blood lust' over trade
It grew into a decades-long friendship that revealed a deeper side of Koko and her ability to understand, though some experts questioned Patterson's methods and Koko's abilities.
We are sad to report that Koko, one of the world's most beloved gorillas, has passed away at the age of 46.More news: Prince Louis to be christened at Chapel Royal, Kensington Palace reveals