The famous primate known for her ability to communicate in sign language first met Robin Williams in 2001. They became friends and years later filmed a public service announcement together. It's being reported that after hearing her trainers discussing Robin's death, Koko became somber and started singing "cry, cry" over and over. The trainers say she looked very quiet and thoughtful after getting the news then appeared sad and withdrawn for the rest of the day. You know you were something special when even other species mourn your passing. Check out this video of Robin Williams and Koko together.