What we found is "hellhound," a demonic dog of hell, found in mythology, folklore and fiction.
It appeared in Piers Anthony’s ‘On A Pale Horse”, wherein Satan sends hellhounds to attack Zane (Death) and bring him back to hell. The hounds are immortal but are dispatched by Death’s magical scythe.
The most famous hellhound is probably Cerberus, the hound of Hades from Greek mythology. Cerberus is a multi-headed dog which guards the gates of Hades, to prevent those who have crossed the river Styx from ever escaping.
As with most creatures from classical mythology, the depiction and background surrounding Cerberus often differed across various works by different authors of the era, the most notable difference being his number of heads; while most sources describe or depict three heads, others show him with two or even just one, a lesser number show a variable amount, sometimes as high as 50.
Want to learn more about Greek Mythology? Check out illustrated biographies of the gods, spirits, creatures and heroes of Greek mythology at Theoi.com.