Ko-Ko was a female gorilla who was able to comunicate thru sign language with her keepers through a computer keyboard with symbols on it.
Zappa dedicated The Real Frank Zappa Book to his wife, children, Stephen Hawking and Ko-Ko. Peter Occhiogrosso, who wrote the book together with Zappa claimed in an interview that the inclusion of Hawking and Ko-Ko might be linked due to the fact that both of them use computer keyboards to communicate with the world. Zappa himself used a computer keyboard as well: the Synclavier.
A different "Ko-Ko" is referenced in Broken Hearts Are For Assholes: "You were dazzled by the exciting new costume of Ko-Ko." This could be a reference to fashion designer Coco Chanel.