Agent Wilson is a timid walrus who works for the walrus society, and he is also Wallree's best friend. He is another main character in the series. He is younger than Wallree but his tusks are longer than Wallree's. He first appears in Book 3, The Trick of Saint Nick. He is always determined to make Wallree and Wendy happy and isn't afraid to take a risk for his friends. Wilson lives in a dorm with Wallree, and Wendy lives next door. In the books he is Wallree's little brother.
- "I'll take care of it, Wallree!"
- "Wallree, watch out!"
- "We used the powers of magnetism!"
- In the movie, Agent Wallree 2 The Hypnotism Hoax, Wilson is played by a seal instead of a walrus.
- In the movie he is played by Harpy Little Harpingsquire.
- In the books he is Wallree's little brother, but in the movie he is not.
- Agent Wilson does not appear in the Agent Wallree radio series.
- In Book 2: The Day My Toaster Attacked, Wilson is mentioned as "Wallree's roommate" and then eaten by a TV. This implies that, when Wallree defeated the electronics, Wilson survived.