Fluffy is the three-headed dog guarding a trapdoor in J.K. Rowling’s Harry Potter and the Philosopher’s Stone.
Hagrid buys Fluffy from a Greek man in a pub and later lends the creature to Hogwarts staff. Fluffy guards the trapdoor leading toward the underground chambers protecting the Philosopher’s Stone. Harry, Ron, and Hermione encounter him while investigating what is hidden beneath the school.
The dog’s weakness is music: playing a tune causes all three heads to fall asleep. Hagrid accidentally reveals this detail to a stranger in the Leaky Cauldron. Fluffy is different from Fang, Hagrid’s boarhound, and from Norbert, the Norwegian Ridgeback dragon Hagrid hatches.