On July 4 in 1971, a primate star is born when a baby western lowland gorilla enters the world at the San Francisco Zoo. The gorilla, born in captivity on Independence Day to parents Jacqueline and Bwana, is named Hanabiko, which means "fireworks child" in Japanese—but she soon becomes known around the world as "Koko."

Koko was full of personality and highly intelligent. As a baby, she caught the attention of Stanford University grad student Francine “Penny” Patterson, an animal psychologist who started teaching Koko sign language. News media covered Koko’s language skills, and the gorilla became a celebrity. Over the years, Koko learned to understand about 2,000 spoken English words, and she could communicate about 1,000 of them using hand signs.

Koko was the subject of many documentaries and articles. In 1978, she appeared on the cover of National Geographic in a photo the gorilla took of herself in a mirror.

In 1983, Koko used sign language to ask for a cat for Christmas. Instead, she got a stuffed animal, but Koko wouldn’t play with it and communicated that she was sad by signing. Later, for her birthday, researchers brought Koko a litter of kittens and let her choose one. She chose a gray and white kitten and named it “All Ball.” The gorilla acted maternally toward the kitten, carrying her like a baby, and even trying to nurse the kitty. Koko and All Ball appeared on the cover of National Geographic in January 1985.

Patterson nurtured Koko and became like a human mother to the gorilla, who moved to Stanford in 1974. In 1986, Patterson started The Gorilla Foundation with biologist Ronald Cohn. The foundation runs Project Koko, which applies the communication lessons learned from Koko and other gorillas to save the species from extinction in the wild and improve gorilla care in captivity.

Koko lived an extraordinary life for more than four decades. On June 19, 2018, Koko died at age 46 in her sleep at the foundation preserve in California’s Santa Cruz Mountains. Koko’s death triggered mourning around the world, and condolences poured into the foundation.

“Koko will make an impact for years to come, possibly generations to come,” an emotional Gary Stanley, acting executive director, told NBC News. “We wanted her to live forever. We were all sort of hoping, secretly.”

Stanley memorialized Koko with this description: “You know she cares about you. She looks it and she says it. She tells you she loves you.”