The Golden Dog
It was an animal sent by Rhea to guard the infant god Zeus and his nurse, the goat Amalthea, on the island of Crete. When Zeus reached maturity, he placed the dog amongst the stars as the constellation Canis Major.
It was a magical dog which was destined to always catch its quarry. It was first given to Europa of Crete by Zeus and then passed down to Minos, Procris, and finally the hero Cephalus.
Cephalus set the hound on the trail of the Teumessian Fox, a monstrous beast ravaging the countryside of Thebes. However, the fox was destined never to be caught, and so Zeus, faced with the paradox of an uncatchable fox being chased by an inescapable hound, turned the pair to stone.
Killed by: Zeus
It was a two-headed, serpent-tailed dog which guarded the fabulous, red cattle of Geryon on the island of Erythea. Heracles was sent to fetch these as one of his Twelve Labours and in the process slew both Orthrus and his master.