Hound of hell

What is the exact meaning of the phrase "a hound of hell" and where does it derive from?

I have to be on a conference call in 1.5 minutes so I can not hit goog but there was a 3 headed monster/hound in Greek mythology who stood outside the gates to the underworld. His name was something like Cerebeus?

THE HOUNDS OF HELL
Meaning: Allegory for evil, or the pursuit by evil

Greek Myth: Again, in reference to Hades's kingdom, Cerberus was a dog who guarded the entrance to the netherworld. There weren't really any "hounds", but Cerberus is often depicted with three-sometimes fifty-heads.