WOODSIDE, CALIFORNIA — Koko, the gorilla famed for her ability to communicate using American Sign Language and amazing friendships with pets, died in her sleep last week at age 46.

Koko was a western lowland gorilla born at the San Francisco Zoo in 1971. She soon formed a close bond with Dr. Francine "Penny" Patterson.

The following year, Dr. Patterson started teaching Koko sign language as part of a Stanford University project.

Koko was said to have an IQ of between 75 and 95, could understand 2,000 words of spoken English. The average IQ for humans is 100, with most people scoring somewhere between 85 and 115.

Koko adopted several cats, and used sign language to give them names. She even grieved for one of her kittens when it was killed in a car accident.

Koko's love of animals turned into a children's book called "Koko's Kitten" and her own line of toys. Due to her fame, Koko became the subject of many documentaries and was on the cover of National Geographic.

Koko also met quite a few celebrities, from the late actor Robin Williams, Betty White, Leonardo Dicaprio, and her favourite celebrity Fred Rogers.