Koko, the beloved gorilla who captivated many with her ability to communicate through sign language, has died at age 46. The western lowland gorilla died in her sleep Tuesday morning, NPR reports. Born at the San Francisco Zoo on July 4, 1971, Koko was chosen as an infant to work with psychologist Francine "Penny" Patterson on a language research project. Her knowledge of sign language offered a window into a gorilla's emotions, such as her affection for her pet kitten and her grief when Robin Williams, whom she once met, died. The Gorilla Foundation, which studied her, announced her passing Thursday, Reuters reports. She died at the foundation's preserve in California's Santa Cruz Mountains, the AP reports.
Koko was twice featured on the cover of National Geographic, including one cover image she snapped of herself; had multiple books written about her; and was featured in several documentaries. She was also the subject of much research—in addition to knowing sign language, for example, scientists studied her and found that apes may be closer to speaking than had previously been though. She learned to play the recorder in 2012, showing that she could control her breathing, which until then primates weren't believed able to do. She was said to understand some spoken English as well as signs. She even once took part in an "interspecies chat" on the internet. Thousands were mourning her death on the Gorilla Foundation's Facebook page. (Read more gorilla stories.)