Where did Hagrid get Fluffy?

Answer 1

Fluffy has three heads and was guarding the Philosopher's Stone. Fluffy is reminiscent to the three-headed dog Cerberus from Greek Mythology. There's no racial name for these creatures, so most people just call them Cerberus.

Answer 2

In the book, Hagrid said he "bought him off a Greek chappie I met in the pub las' year." The seller's nationality is, of course, a nod to Cerberus being from Greek mythology. For some reason, Hagrid's line was changed in the movie, replacing "Greek chappie" with "Irish fellow" and thus cutting the book's mythological in-joke.

Answer 3

It has three heads, it is much larger than normal dogs and it falls asleep when it hears music.

Answer 4

Fluffy was described as "a monstrous dog" that was as tall as the room, had three heads. Fluffy had three pairs of eyes, three noses, three drooling mouths each with yellow fangs.

Answer 5

They play music until he falls asleep.

This is also what Orpheus did to Cerberus in the Greek myth.