Koko the gorilla, whose language skills stunned and charmed the world, has passed away at the age of 46. Koko could communicate in sign language, and had a reported vocabulary of about 2,000 words. She also displayed emotions like empathy and affection. Her talent was the subject of many documentaries, and she was featured twice on the cover of National Geographic. Some scientists questioned whether her abilities were exaggerated and her emotions were faked or imagined. But Koko remained a world-wide star.
Watch Koko learn and use sign language: