Wikipedia: Hanabiko “Koko” (born July 4, 1971) is a female western lowland gorilla who is known for having learned a large number of hand signs from a modified version of American Sign Language.

Her trainer, Francine “Penny” Patterson, reports that Koko is able to understand more than 1,000 signs of what Patterson calls “Gorilla Sign Language” (GSL).^[2] In contrast to other experiments attempting to teach sign language to non-human primates, Patterson simultaneously exposed Koko to spoken English from an early age.

Reports state that Koko understands approximately 2,000 words of spoken English, in addition to the signs.^[3] Koko’s life and learning process has been described by her trainer Patterson and some of her collaborators in a number of books, peer reviewed articles, and on the website http://natureseeyou.com