Cleo is Geppetto's pet goldfish from Pinocchio.
Cleo is always seen in her fishbowl, often reacting or responding to a situation through silent smiles and water twirls. She appears to be very affectionate, specifically towards Geppetto and Figaro (who seems to hold a mild dislike towards her). When asked by Geppetto whether or not the name "Pinocchio" sounds any good for his latest puppet creation, Cleo shows her distaste, but the name goes through anyway.
Later on, when Pinocchio is given life, he's sent off to school along with the other children. Excited to have a family, Geppetto sets up a delicious dinner, including a small piece of cake for Cleo. Unfortunately, Pinocchio doesn't return, resulting in Cleo, Geppetto, and Figaro heading out to find them. The trio ends up in the belly of Monstro the whale, and eventually give up any hope of escape. As such, Cleo begins to build her own tombstones, knowing she'll perish, along with her loved ones, should they not escape or manage to eat. Surprisingly, Pinocchio arrives and concocts a way to free them. The plan succeeds but results in Pinocchio's demise. Geppetto, Cleo, and the others return to their village home and mourn the death of the little wooden boy, only to find his act of bravery granted his revival (via the Blue Fairy).
Once this realization dons upon Cleo and the others, a celebration is held.