Cerberus is best known for playing a part in Hercules' final labor. Hercules had to go to the Underworld and bring Cerberus back to the surface of the earth without using his arrows or his club.
Hercules grabbed Cerberus by the throat and dragged him to Mycenae through a crack in the surface of the earth. Having accomplished this, Hercules dispatched Cerberus to guard one of the secret groves of Demeter but the dog eventually made his way back to Hades where he still guards the entrance.
In another legend, Orpheus makes the same journey to the underworld to bring back his lover, Eurydice. He manages to soothe Cerberus with his lyre.
In the Aeneid, the Trojan hero, Aeneas descends to Tartarus to visit his father Anchises. He is escorted by the Bybil of Cumae, and upon encountering 'huge Cerberus barking from his triple jaws, stretched at his enormous length in a den that fronts the gate,' she throws him a cake seasoned with honey and poppy seeds. Now Cerberus, “his neck bristling with horrid snakes, opening his three mouths in the mad rage of hunger, snatches the offered morsel, and spreads on the ground, relaxes his enormous limbs, lies now extended at the vast length over all the cave. Aeneas, now that hell's keeper is buried in sleep, seizes the passage and swiftly over-passes the bank of that flood whence there is no return.”
Virgil described him by saying:
'No sooner landed, in his den they found the Triple porter of the Stygian sound, Grim Cerberus, who soon began to rear His crested Snakes, and armed His bristling hair.'
'Orcus' warder, blood-besmeared, Growling o'er gory bones half-cleared Down in his gloomy den.'
In Dante's Inferno, Cerberus was the tormenting genius of the third circle. There the gluttonous and incontinent souls could be found immersed in turbid water. Hail and snow poured down through the dark air upon their grimacing faces. Cerberus took care to see that each soul received its due share of torment:
'Cerberus, a monster fierce and strange, with three throats, barks dog-like over those that are immersed in it. His eyes are red, his beard greasy and black, his belly wide, and clawed his hands; he clutches the spirits, flays and piecemeal renders them. When Cerberus, the great Worm, perceived us, he opened his mouth and showed his tusks: no limb of him kept still. My guide, spreading his palms, took up earth; and, with full fists, cast it into his ravening gullets. As the dog, that barking craves, and grows quiet when he bites his food, for he strains and battles only to devour it: so did those squalid visages of Cerberus the Demon, who thunders on the spirits so, that they would fain be deaf.'