Found in both Roman and Greek mythology. Usually depicted as a dog with three heads it has also been described as having about fifty heads. It is said to have a snake for a tail and often many snake heads growing from its back. Less seldom Cerberus has also been depicted as having one head of a man and the other two of a dog. It has encountered Greek and Roman Heroes : Hercules and Aeneas. It is the offspring of Tyophon and Echidna. Echidna was half woman and half serpent. Cerberus is the guardian of the underworld.
Taken from a translation of John Ciardi's from Dante's The Inferno.
"Cerberus, the ravenous three-headed
dog of Hell, stands guard over
them [souls],
ripping and tearing them with his
claws and teeth...
slavers over them [Gluttons] as
they in life slavered over
their food..."
"Here monstrous Cerberus, the ravening
beast,
howls through his triple throats
like a mad dog
over the spirits sunk in that foul
paste."
"His eyes are red, his beard is
greased with phlegm,
his belly is swollen, and his hands
are claws
to rip the wretched and flay and
mangle them [souls]."
"When Cerberus discovered us in
that swill [Dante and Virgil]
his dragon-jaws yawed wide, his
lips drew back
in a grin of fangs. No limb of
him was still."
-THE INFERNO
Dante's immortal drama of a journey
through hell.
As you can see some of the description are quite colorful, sometimes in a discusting way, but still the book is quite interesting. I enjoyed reading it.