In Monsters, Inc., the friendly blue monster is Sulley, whose full name is James Patrick Sullivan. Sulley is a large, furry monster with cyan-blue fur, purple spots, horns, and a gentle personality that contrasts with his intimidating appearance. He works as a professional scarer at the Monsters, Inc. factory and is partnered with the much smaller Mike Wazowski.
At first, Sulley is focused on maintaining his reputation as one of the factory’s top scarers. His outlook changes after a human child, nicknamed Boo, accidentally enters the monster world. Sulley initially fears the consequences of contact with a child, but he gradually becomes protective of Boo and challenges the factory’s assumptions about fear and human children.
Mike is Sulley’s green, one-eyed best friend and assistant, while Randall Boggs is his purple, camouflage-capable rival. Boo is a human child, not a monster. The character is commonly called “Sulley,” although “Sullivan” also appears in his full name and workplace identity. His kindness ultimately helps transform Monsters, Inc. from a fear-powered factory into one powered by laughter.