World War II is a cat owned by Charlie Brown's neighbor. He is a rival of Snoopy and Woodstock. He is a sadistic and homicidal cat that is always in pursuit of hunting down Snoopy, but Snoopy usually outsmarts the cat. The cat has attacked Snoopy and Woodstock several times, but has also attacked Spike, Peppermint Patty, and Marcie. He is a dangerous and powerful cat, but he isn't very smart.
World War II has done many things to Snoopy and Woodstock over the years. He has done mild things like scratched them and swiping their food, to more extreme stuff like destroying their house or breaking Snoopy's leg.