Fluffy is the three-headed dog guarding a trapdoor in J.K. Rowling’s first Harry Potter novel.
Hagrid keeps Fluffy in Hogwarts as part of the protection around the Philosopher’s Stone. The enormous dog stands above a trapdoor and is intended to prevent unauthorized people from reaching the challenges below. Harry, Ron, and Hermione eventually discover that music can make Fluffy fall asleep.
Fluffy’s name is deliberately comic in contrast with his frightening appearance. The character is based on Cerberus, the three-headed guard dog of the underworld in Greek mythology. Rowling’s use of this classical reference reflects her interest in mythology and classical studies.
Fang is Hagrid’s large but ordinary dog, while Norbert is a dragon and Aragog is an enormous Acromantula. These creatures are all associated with Hagrid, which makes the names easy to mix up, but only Fluffy guards the trapdoor.