PJ is the ghost of a young boy who lives in Max's House above the Corner Store. He died at age 11 of unknown causes, and seems to have significant self-confidence issues. PJ is his given name and has nothing to do with the fact that he died in his pajamas.
Personality
PJ is a timid individual lacking the self confidence and incredibly awkward. He is also very depressed, often practicing smiling to prepare for a time he can feel actual happiness again. He wants to be a poltergeist and move corporeal objects and looks up to Max as a sort of superhero for being able to fend off people older than him.
Relationships
Maxwell Puckett
He and Max are friends, though PJ's self-confidence issues often get in the way of their friendship's development. Max sometimes gives PJ words of encouragement, but he is just as likely to accidentally disregard or insult the poor ghost.
Lefty
PJ has been friends with Lefty since before the comic started with the latter seemingly acting as PJ's guardian and protector from more malevolent spirits.
Hissin' Pete
Pete seems to be in some degree friends with PJ and Lefty, although he hasn't interacted much with them save for clinging to PJ in fear.