Koko is a 35 year-old lowland gorilla who learned to speak American Sign Language when she was just a baby. Her teacher, Dr. Penny Patterson, began working with Koko as a Ph.D. project at Stanford, thinking it would only be a 4-year study.
Thirty-some years later, Penny and Koko continue to work together at the Gorilla Foundation in one of the longest interspecies communication studies ever conducted, the only one with gorillas. Koko now has a vocabulary of over 1000 signs, and understands even more spoken English.
Koko has become famous not only for her language capabilities, but also her heart-warming relationship with kittens (captured in the book Koko's Kitten). As Penny says, "she's just as much a person as we are."