Koko learned over 1,000 signs and understood 2,000 English words, and exhibited self-awareness by recognizing her own reflection in the mirror — and these kinds of achievements shot the gorilla to fame. She graced the cover of magazines and was featured in several documentaries. She met celebrities like Leonardo DiCaprio and the late Robin Williams.
In 1974, Koko even got her own kitten, All Ball, after asking her caretakers with sign language for a kitten the previous Christmas. Koko was gentle with All Ball, carrying her around like a baby and even trying to nurse her. All Ball sadly passed away, and when caretakers told Koko about the death, she began to whimper and make a hooting noise — a sign that she was grieving.