Walter John Wolf is Slappy Squirrel's biggest arch-enemy and the main antagonist in the Slappy Squirrel segment, often trying to defeat Slappy in various ways, including filing a false assault lawsuit against her (...And Justice for Slappy) or faking his death to ambush Slappy at his "funeral" (Rest in Pieces ), but he always fails in his plans. Sometimes, he teams up with Slappy's other long-time foes, like Sid the Squid and Beanie the Brain-Dead Bison. His grandson is Stephen Wolf (...And Justice For Slappy). He was voiced by Frank Welker in his first appearance and Jess Harnell in the rest of his appearances. Both actors gave Walter a Yiddish accent. He is the most prominent antagonist that has appeared in the Slappy Squirrel segment.
In the comics, it was revealed he was the star of a TV show that only lasted for 8 episodes, with Slappy Squirrel as his sidekick.
- Slappy Goes Walnuts (young, seen in old Slappy cartoon; nonspeaking)
- Episode 16: Chalkboard Bungle/Hurray for Slappy/The Great Wakkorotti: The Master & His Music
- Episode 40: Casablanca Opening/Fair Game/The Slapper/Puppet Rulers
- Episode 45: Mary Tyler Dot Song/Windsor Hassle/...And Justice for Slappy
- Episode 62: Scare Happy Slappy/Witch One/MacBeth
- Episode 64: Lookit the Fuzzy Heads/No Face Like Home
- Episode 72: Deduces Wild/Rest in Pieces/U.N. Me
- Episode 83: One Flew Over the Cuckoo Clock
- Episode 99: Birds on a Wire/The Scoring Session/The Animaniacs Suite
- Episode 5 (Reboot): Good Warner Hunting/No Brainer/Ralph Cam (nonspeaking cameo)