Snowball V

Snowball V (a fictional character in the television series The Simpsons) is Lisa Simpson's cat, which she obtained as a result of a succession of her cats dying in the 15th season episode, I,(Annoyed Grunt)-bot (see The Simpsons episode list). Snowball II was hit by a Mercedes-Benz driven by Dr. Julius Hibbert. Lisa then went to an animal refuge, where she got Snowball III. Snowball III drowned while trying the catch the fish in the aquarium. After the death of her next cat, Coltrane, Lisa gave up on cats, but the crazy cat lady gave her another cat, which ran into the street after Lisa shooed her away. A car, driven by Gil, came close to running her over, but he swerved and hit a tree (which then humorously caught on fire). Lisa, taking this as a good omen, took the cat and named her Snowball V, but to 'save from buying another dish' she called her Snowball II.

More than likely, the name choice was done to preserve the status quo of the episodic series.