. . . yes, Koko's passing made me sad. I was always fascinated by Koko (and by extension, animal intelligence) growing up. She appeared twice on the cover of NGM (1978 & 1985).
I remember seeing the 1985 cover at my Grandma's when I was 7. Koko's NGM debut was my birth year.
I believe that only Jane Goodall has appeared (3 times) on the cover more than Koko (2) has.