In 2001, Robin Williams had the chance to meet Koko the Gorilla who uses sign language at the Gorilla Foundation in California. After meeting, they became special friends.
Six months prior to meeting, Koko lost her male companion of 27 years. She was devasted and seemed depressed. When Williams interacted with her, she suddenly cheered up and started smiling.
As you'll see in the video, they bonded. Upon Williams passing on Monday, the staff doctors signed to Koko that he had died. Throughout the day, Koko became very somber with her head bowed and lip quivering. Watch the amazing interaction between Williams and Koko in 2001.