Cerberus

You may recognize this creature from Harry Potter.  He is Hagrid's Fluffy.  "Cerberus was the monstrous three-headed dog who guarded the gates to the underworld, according to Greek mythology.  Instead of fur, Cerberus had a coat of writhing snakes - presumably taking all the pleasure out of scratching." (Jeffrey C. Cole, Eyeball Animation Drawing Book: Creatures Edition.  Accord Publishing Ltd.  Denver.  2002.)

If you want to learn more about this mythological creature, you can read about it at Wikipedia here.