Number Four is the primary large feline minion of Bob the Killer Goldfish. He appears to have no will of his own, simply doing what Bob requires. He is granted the right to carry Bob on his shoulders, a prestigious honor. Number Four is often seen operating the control panels in Bob's Warfish starship, and essentially carrying out any task that Bob, in his limited capacity, cannot.
It is revealed in both the games and the animated series that there had been previous minions similar to Number Four (Numbers One, Two, and Three, although Bob neglects to give any information other than that they have suffered a "rather painful" fate), and that there are feline minions above him as well (Numbers Five, Six, and Seven). They all appeared in one episode of the animated series, where Number Seven joined Numbers One, Two, and Three in Kitty Heaven ("Where the milk flows like waterfalls, and the mice are slow.") after placing an atomic missile into an oven. Ironically, the cats of Kitty Heaven are utterly bored since the slow mice offer no sport.
Number Four appears as an enemy in both Earthworm Jim and Earthworm Jim 2. In the first game, he paces back and forth through the corridors of Bob's underwater base on La Planeta de Agua (Arriba!) in Down the Tubes. He will choke and punch Earthworm Jim if he catches him, knocking him back and doing heavy damage. He can block all of Jim's attacks with his forearms, but a single bite from the Hamster will destroy him. In the second game, Number Four can be seen practicing his bowling skills (with a fishbowl) in Anything But Tangerines. Jim can defeat him by hitting padlocks above his head, which will bury him under an avalanche of trash.