World War II, also known as "The Cat Next Door", is an unseen cat character that terrorizes Snoopy and Woodstock. Whenever Snoopy mocks the cat from across the yard, the cat slashes Snoopy's doghouse or sometimes, him.Charlie Brown usually ends up having to buy another doghouse, as a result.
Occassionlly, Snoopy will attack the cat "off-stage" if someone (such as Woodstock) is in mortal danger. However, Snoopy's attacks usually result in him looking beaten up or scratched when he reappears.
World War II's paw has been shown briefly a few times in The Charlie Brown and Snoopy Show, in the sections "Snoopy's Foot" and "Blanket" (The short that consist of Snoopy and Linus van Pelt trying to retrieve Linus' blanket back from next door after Sally Brown's friend Eudora gave it away to the cat). His paw appeared as orange in "Snoopy's Foot" but was white in "Blanket".