Koko, a world-renowned western lowland gorilla (Gorilla gorilla gorilla), passed away June 19, 2018 at her home at The Gorilla Foundation (TGF) in Woodside, California at the age of 46. Born at the San Francisco Zoo to mother Jacqueline and father Bwana on July 4th, 1971, she was named Hanabi Ko, Japanese for fireworks child, which was later shortened to Koko. Separated from her gorilla group due to illness before her first birthday, she was raised by humans: first at the Zoo, then at Stanford University (1974), and after being purchased from the Zoo by The Gorilla Foundation in 1977, finally at a six and one-half acre compound in the hills of Woodside, California (1979). Koko was probably the most documented individual non-human animal (over 45 years), and was most famous for being the first gorilla to communicate via a modified version of American Sign Language (ASL). She began to learn ASL at the age of one from Francine (Penny) Patterson, a Ph.D. student at Stanford University. From this point on, Penny and Koko would spend the rest of Koko's life together. In the 1960's and 1970's several university research projects began to study human-reared apes as models for a window into early human development and language acquisition. Most of these featured chimpanzees, including Washoe (who was taught ASL), inspiring Patterson to begin Project Koko (Patterson & Linden, 1981). While the conclusions of these studies may have provided some basis for the understanding of the development of human language, many of these apes were retired at a young age when the studies ended, relegated to a long life in labs or zoos. While separating infant apes from their natal groups for cognitive studies was an acceptable practice during these times, much more has been learned about the negative consequences of social isolation, and now such cognitive studies with infant apes are frowned upon outside of a group setting. In addition to Patterson's Ph.D. thesis (Patterson, 1979), several peer-reviewed articles and even a few Masters’ thesis were based on the studies of Koko (Goodreau, 1987; Watson, 1983). Koko was said to have a working vocabulary of 1,000 signs and understand over 2,000 words of spoken English. The primary method utilized to teach Koko ASL was a “molding” technique (Patterson & Linden, 1981). Every teacher who interacted with Koko was trained to record a daily record of Koko's sign usage on a checklist. In order for a sign to be included as part of her working vocabulary, it had to be signed by Koko in a spontaneous and appropriate use for 14 days in a row. At times Koko had other gorillas to interact with: initially Michael, a three and one-half year old wild-caught orphan from Cameroon, lived with her beginning at the Stanford University site (1976) and continuing at the Woodside site. They had regular visits until he became too strong and aggressive toward her in his teens. He was also taught ASL, and they were observed to spontaneously have conversations with each other (Watson, personal observations). He passed away in 2000. Most likely due to an incest taboo documented in gorillas living together from a young age (Stewart & Harcourt, 1987), they never reproduced. Another adult male, Ndume, was brought to Woodside from the Cincinnati Zoo as a proposed mate for Koko in 1991, yet their pairing never led to Koko having an infant. Ndume and Koko remained neighbors, housed in adjoining facilities, until her passing. Koko began life as an ordinary captive-born gorilla, but her celebrity grew as people began to hear about this young gorilla that was learning sign language, and she became famous through press coverage. Koko's intelligence and interactions with humans captured the fascination of a worldwide audience. Koko inspired millions of people around the world to better understand the sensitive, caring and intelligent nature of gorillas, and became an ambassador for her species through many magazine articles, books, documentaries, news stories, public service announcements, a website, photos, and film/video clips on YouTube and the internet. She participated in the first Interspecies Internet Chat on AOL (1998), and even collaborated with Apple™, that in 1988 built her a computer with a prototype touch screen to enable her to have a “voice” (Summers, 1993). The computer screen had images that when touched would verbalize the objects’ names. Patterson and Eugene Linden co-wrote a book “The Education of Koko” in 1981 (Patterson & Linden, 1981) documenting her work during the first 8 years of Project Koko. Koko was featured in two cover stories for National Geographic magazine, first in 1978 featuring a cover self-portrait photo taken in a mirror by Koko (Patterson, 1978). The second article (Vessels, 1985), told the story of her relationship with a kitten named All Ball, with whom she had supervised visits. Unfortunately, one day the cat snuck out a door during a rainstorm and was later found dead, hit by a car. When told about All Ball's death, Koko reportedly displayed evidence of sadness and mourning. This amazing story with accompanying photographs spread around the world. In late 1985 Patterson wrote the book “Koko's Kitten” (Patterson, 1985) to tell the story, highlighting the gentle nature of gorillas and Koko's intelligence, ability to use sign language for communication, and her empathy for other living things. Koko's Kitten would later be published in Braille (1995), French (1997), and Japanese (2002). Over 20,000 copies of the French and English versions were distributed in gorilla range countries, such as Cameroon, and used as curricula in schools throughout the United States and Africa. This story reached the hearts of humans worldwide, demonstrating a gorilla's capacity for tenderness and grief, enlightening the general public about how gentle gorillas can be, and helping dispel the King Kong myth. Koko's story had a profound effect on people, leading to conservation learning and affective change in how the public felt about, and acted toward gorillas. Some former gorilla hunters even converted to gorilla conservation rangers after exposure to Koko's story (Rose, 2000). Four documentaries were made of Koko during her life beginning with 1978's Koko: A Talking Gorilla (Schroeder, 1978). The last documentary, Koko: The Gorilla Who Talks (Taylor, 2016) was released in 2016 in the UK and 2017 in the United States. She was also featured in thousands of newspaper articles and television newscasts worldwide through the years, and even in features on CBS's 60 min and ABC's 20/20 news magazines. Koko also had visits with celebrities such as Robin Williams, Peter Gabriel, Mr. Rogers, Betty White, William Shatner, Sting, and Leonardo DiCaprio, and scientists including Dian Fossey, Jane Goodall, and Richard Wrangham, garnering tens of millions of views on YouTube (You Tube, 2018a) and over 250,000 followers on her Facebook page (The Gorilla Foundation, 2018). At one point The Gorilla Foundation had over 45,000 members (The Gorilla Foundation, 2005), and there is even a You Tube channel devoted to Koko (You Tube, 2018b). Koko's life was not without controversies. Some of the research methodologies and results of studies with Koko were questioned by the scientific community, leading to fewer and fewer peer-reviewed publications and an eventual dearth of grant funding. This led to Project Koko fading from the medias’ eye and the scientific community as TGF pulled back from communicating on their work with Koko. Over the years more than a hundred caregivers, volunteers, and teachers had the opportunity to work with Koko during her lifetime. She touched and inspired everyone she met in many ways with her exuberance, playfulness, sense of humor, curiosity, and desire to interact. Koko had many fans all over the world; she would get the most wonderful and inspiring letters from children with drawings and stories about how her story had touched them, as well as a multitude of birthday and holiday cards annually. In 2014 while working for TGF, Dr. Gold gave a presentation at the International Gorilla Workshop in Atlanta, and asked the assembled 250 gorilla experts: keepers, researchers, and curators, “who among them had been personally inspired by Koko's story” and about 40% of the attendees raised their hands. Both authors had strong connections with Koko and memories of her uniqueness. Dr Watson worked with Koko from 1979 to 1983 (Koko was 9–13 years old), a time of intense study and research. Watson's M.A. thesis centered on correlating Koko's estrous cycles with Koko's overt social behaviors (Watson, 1984). Dr. Watson recounts the times when Dr. Patterson and herself would walk Koko around Stanford University Medical Center. This was done on Sunday afternoons when there were few people about, and later, their walks into the woods around the Woodside facility. Koko would always be the first to hear an animal, or feel the earth move: just before a mild earthquake hit; or the first to hear some very distant sound. To Dr. Watson, this highlighted how most humans, especially in first-world cultures, are removed from their environment. Many years later when working in Africa studying wild-living lowland gorillas, Dr. Watson could not help but recall those moments with Koko and how much Koko taught her about being attuned to one's environment. Koko has had a profound effect on her throughout her career; and she still does. Dr. Gold worked with Koko much later in her life from 2013 to 2015, when she was 42–44 years old, and had slowed down from her youthful research projects, preferring to spend most of her day resting. As Dr. Gold was not fluent in ASL, he would often speak to Koko in English, some of which she seemed to understand. One specific memory altered his skepticism about Koko's ability to understand English. One day he was in her trailer sitting with only chain-link separating them as it poured rain outside. Among her many blankets, toys, books, and assorted clothing in her enclosure he noticed a yellow slicker raincoat that humans would wear. He offhandedly said something like “Koko, I see you have a raincoat, but I'll bet your arms don't fit inside, since it is made for people.” After turning around to arrange some items in the trailer's kitchen, he turned back to observe that Koko had taken the raincoat from among a pile of belongings and was putting her arm into it. Needless to say, this shocked him, giving him insight into her understanding of not just words as objects, but as objects and actions. Dr. Gold, having worked many years on film sets with very well trained animals, realized that Koko was not just a trained gorilla that could understand and perform to commands; she was a cognizant being who could truly understand him. Koko will be missed for her unique personality, gentle spirit, and inspiration to humanity worldwide.