Gorilla most proficient in sign language

In 1972, Koko, a western lowland gorilla, was taught Ameslan (American Sign Language for the Deaf) by Dr. Francine Patterson. By 2000, Koko had a working vocabulary of over 1000 signs and understood approximately 2,000 words of spoken English. She could refer to the past and future, argue, joke and lie. When Koko was asked by Dr. Patterson whether she was an animal or a person, she replied "fine animal gorilla."

Koko was born Hanabi-ko (Japanese for “Fireworks Child”) on 4 July 1971 at the San Francisco Zoo. She passed away in her sleep on 19 June 2018 at The Gorilla Foundation's preserve in California's Santa Cruz mountains aged 46 years 350 days.