In 2001, Robin Williams met Koko, the gorilla who communicates in sign language, at The Gorilla Foundation in Woodside, Calif. The two immediately became friends.
"Koko instantly connected with Robin," said Dr. Penny Patterson, the foundation's president and the gorilla's foster mother. "Koko, like us, can sense a person's nature and in this case, she was quickly drawn to Robin's warm heart."
The actor, who would later describe the meeting as "unforgettable," filmed a PSA with Koko for the foundation in 2004 to raise awareness of environmental threats to the species. Williams also accepted the post of honorary co-chair for the foundation's campaign to create the Maui Ape Preserve.
On Monday, Koko was with Patterson when news of Williams' death broke and phone calls started to come in.
"After the first call, Koko came to Dr. Patterson with an inquiring look on her face. Dr. Patterson explained that 'we have lost a dear friend, Robin Williams.'"
"Koko was quiet and looked very thoughtful," a spokesperson for the Gorilla Foundation said in a press release emailed in response to an inquiry from BuzzFeed.
"Koko became very somber, with her head bowed and her lip quivering."
On Tuesday, the Gorilla Foundation posted a message of remembrance and a video of the actor's meeting with Koko to honor his life, "which was a profound gift to humanity — and to other great apes like Koko."
"Not only did Robin cheer up Koko, the effect was mutual, and Robin seemed transformed — from a high-energy entertainer, into a mellow, sensitive, empathetic guy, who also happened to be really funny."
Watch the heartwarming video of the actor's meeting with Koko.
Ellie Hall is a reporter for BuzzFeed News and is based in Washington, DC.