Koko is said to be "extremely sad" over news that Williams had died.
The Gorilla Foundation, like so many others, offer their condolences -- but at the same time ask people to celebrate all he did on behalf of gorillas, like Koko:
"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. Robin's ability to just 'hang out' with Koko, a gorilla, and in minutes become one of her closest friends, was extraordinary and unforgettable for Koko.
"And when you remember Robin Williams, remember that he is not only one of the world's most beloved entertainers, he is also one of the world's most powerful ambassadors for great ape conservation."