The blue furry monster in Monsters, Inc. is Sulley. His full name is James P. Sullivan, and he is the film’s leading scarer and one of its two central heroes.
Sulley is a massive, gentle monster covered in cyan-blue fur with purple spots. Although his size and job are meant to frighten children, he is kind-hearted and quickly becomes protective of Boo, the human child who accidentally enters the monster world. His friendship with Mike Wazowski drives the story.
A common mix-up is confusing Sulley with Randall Boggs, his purple, reptile-like rival. Randall can camouflage himself and schemes to use a machine that extracts children’s screams. Mike is Sulley’s short, green, one-eyed assistant and best friend, while Boo is the child they try to return home.
Sulley’s character also appears in the prequel Monsters University, which shows how his rivalry with Mike gradually becomes a lasting friendship. John Goodman provides Sulley’s voice in the main film series.