James Phil Sullivan, better known as Sulley, is the main protagonist of Monsters, Inc. and Monsters University. He is Mike's best friend and the current CEO of the company.
Sulley reappears in the prequel as an 18-year-old teenager, nicknamed Jimmy Sullivan in college.
James P. Sullivan was a monster in Monstropolis, a city where the citizens were monsters. The city was going through an energy crisis, so to get energy monsters would go to the human would and scare children and collect their screams to provide energy. However, they thought children were toxic so they would do this without coming into physical contact with the child. For several years this went on, with Sullivan being the top scarer. Unknown to Sulley, one of the other scarers, Randall Boggs, wanted to be top scarer. During one scaring, the CDA was called when a sock became stuck to one monster. After the scaring, Sulley saw Randall sneaking into a room with canisters filled with childrens screams. After Randall left, a young girl sneaked into the monster world. Sullivan initially tried to bring her back to her room and then tried to hide her in a bag, but she escaped and was spotted. She was put on the newspapers, and the CDA was sent to find her. Sulley and Mike kept Boo hidden in their room so that nobody found her, and Sulley named her Boo.
- Sulley is constantly thought to be the deuteragonist of Monsters University.