You may be looking for a different Max. See Disambiguation Max For more information.
Max Johnson is the nephew of the late Chester Johnson.
Max was very close to his uncle, Chester, and when his mother attempted to donate all of Chester's costumes, he pleaded with her not to. His mother did not listen.
A couple of months after his uncle's death, Max finds his mother talking to the police on their doorstep. He asks her why they are here, ignoring her pleas for him to go inside and finish his homework.
Donna offers to show him her police car, and let him try out the radio, much to his excitement.
Later on, the police - in reality, Dean and Sam Winchester - return to the house at night and are greeted by Max. Max tells Dean his mother isn't home yet, so Dean asks to wait inside and starts asking Max some questions.
Max admits he still misses his uncle, who taught him a few magic tricks. He tells Dean that "those men" said untrue things about his uncle. Just then, Rita returns with Sam right behind her. She is unhappy with Dean's private talk with Max, and orders Max to leave the room.
While Dean and Sam confront Rita about the truth, Max puts on a deer head once belonging to Chester, which allows Chester's spirit to possess him and attack the three. Before he can kill Rita, Dean manages to get the deer head off and sends Sam to burn it. A confused Max asks his mother what's going on.
Dean makes a salt circle around Max and his mother, and orders them to stay inside. He reveals to them that Chester has returned as a vengeful spirit. Chester soon manifests and attacks Dean. Max tries to call out to him, but Chester is only momentarily distracted before he gets angry again.
Chester is defeated once Sam burns his deer head mask. Later on, Rita and Max are spoken to by Officer Doug Stover, while Dean, Sam and Donna exit the house.