In Pixar’s Monsters, Inc., Sulley’s full first name is James.
The character is formally named James P. Sullivan, although nearly everyone in Monstropolis calls him Sulley. His surname connects him to the large blue monster’s identity as the film’s most famous scarer and the central character alongside Mike Wazowski.
The name is easy to miss because the film’s dialogue overwhelmingly uses “Sulley.” It appears in professional and official contexts, including his work records and the company’s interactions with him. Mike’s full name is Michael Wazowski, so the two friends have distinctly different naming patterns.
James P. Sullivan begins the story as Monsters, Inc.’s top scarer, but his attitude changes after Boo enters the monster world. By the ending, he becomes central to replacing fear-based energy collection with laughter-based energy.