Koko is a gorilla living in the San Francisco Zoo, who knows how to communicate using a basic form sign language. She was born in 1971.

Her instructor, Francine Patterson, trained her from age 1, and reports that Koko now understands more than 1000 signs of "Gorilla Sign Language", and understands 2000 spoken English words. Patterson reports that Koko makes up new signs, can combine multiple signs in a meaningful way, use humor and meta language. It is debated how complex her language actually is - she doesn't seem to use consistent grammar, and her use of language does not seem to exceed that of a young human child.

Koko passed the mirror test when she was 19, where a colorful dot was glued to her forehead. When looking in a mirror, she realized that she saw herself and investigated the dot. Most other gorillas fail this test.

She also is one of the few non-humans known to keep pets: For christmas 1983, she asked for a cat, later named it "All Ball", and cared for it as if it were a baby gorilla.