He has the appearance of a prize-winning show-cat and an obstinate attitude toward anything he does not like. He often goes out of his way to annoy or embarrass female humans he does not approve of. He also has a habit of watching birds and knocking books off shelves, and these books are normally read to the cats by Qwilleran. Though it would seem he would be able to do fine on his own, when Qwill had to go to work, Koko became lonely and this led to Qwill to get Yum Yum. Of course, because Koko eats food like salmon and crab, Yum Yum had the privilege of eating this food as well. Qwilleran always feeds them such meals throughout the series.