Koko was a small, white alien monkey that lived aboard Brainiac's star ship. Brainiac kept Koko as a pet and frequently brought him along on many of his conquests. Koko provided an attentive ear when Brainiac felt the need to engage in long-winded soliloquies.
Post-Crisis, a larger, more ferocious version of Koko lived aboard Brainiac's ship, and fought Superman. Superman commented that this version was likely one of Brainiac's genetic experiments. In the 31st century, Brainiac's descendant, Brainiac 5, owned a small pet monkey named Koko.