The Gorilla Foundation says her ability to use sign language to communicate with humans demonstrated the species' emotional capacity and made a huge impact.
"People's lives were changed completely after meeting her, they looked in her eyes and it was almost like another universe," said Joy Chesbrough with the foundation.
Koko brought joy to many people, including celebrities like Flea, the bassist for the Red Hot Chili Peppers.
VIDEO: Watch Koko the gorilla rock out on the guitar
"Coco, you're a very curious gorilla," Flea once said.
Robin Williams also had a big impact on Koko.
Koko's handlers said at that time, she hadn't smiled in six months since her lifelong partner passed away. Williams made her smile.
The two joked and wrestled, even got into a tickling fight.
VIDEO: Koko the gorilla somber after Robin Williams' death
The foundation said Koko expressed sadness after her handlers explained Williams had died in 2014.
The western lowland gorilla was born on July 4, 1971 at the San Francisco Zoo.
In 1972, Dr. Penny Patterson started teaching Koko sign language and eventually established The Gorilla Foundation and moved to the Santa Cruz Mountains. "They developed a bond and couldn't let go. They were like mother and daughter," said Gary Stanley, chief operating officer at the Gorilla Foundation.
With Penny's help, Koko learned to use over 1,000 signs and seemed to understand approximately 2,000 spoken English words.
The foundation says that Penny is heartbroken over the loss. Even Koko's gorilla companion at the compounded, Ndume, is in a sad state, signing "sad." The Gorilla Foundation released a statement overnight, saying, "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 foundatin's headquarters in Redwood City were busy Thursday answering calls from around the world. Their website Koko.org even crashed due to the heavy traffic. They are encouraging people to go to their online page and share stories of how Koko impacted them.
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