In Greek mythology, Cerberus (from Κέρϐερος, Kerberos, demon of the pit), was the hound of Hades—a monstrous three-headed dog (sometimes said to have 50 or 100 heads), (sometimes) with a snake for a tail and innumerable snake heads on his back.
Cape Tenaro is where Heracles went to find the entrance to Hades (or Άδης in Greek) to fulfill his last labor of capturing Cerberus
Heracles with Cerberus
The picture is reproduced from Baumeister's Denkmäler des klassichen Alterthums, volume I., figure 730 (text on p. 663). It is on a vase and describes one of the twelve heroic deeds of Herakles. The latter, holding aloft his club, drags two-headed Cerberus out of Hades by a chain drawn through the jaw of one of his heads. He is just about to pass Cerberus through a portal indicated by an Ionic pillar. To the right Persephone, stepping out of her palace, seems to forbid the rape. Herakles in his turn seems to threaten the goddess, while Hermes, to the left, holds a protecting or restraining arm over him. Athene, with averted face, ready to depart with her protégé, stands in front of four horses hitched to her chariot. Upon her shield the eagle augurs the success of the entire undertaking. Cerberus, The Dog of Hades, Maurice Bloomfield
He guarded the gate to Hades (the Greek underworld) and ensured that the dead could not leave and the living could not enter. His brother was Orthrus.
He was overcome several times:
Orpheus used his musical skills to lull Cerberus to sleep.
In Roman mythology, Aeneas lulled Cerberus to sleep with drugged honeycakes.
In Roman mythology, Psyche also lulled Cerberus to sleep with drugged honeycakes.
In Greek mythology, Hermes puts him to sleep with water from the river Lethe.
He can be found also in Dante's Divine Comedy, in Canto VI of Inferno (third circle).
Cerberus has also made numerous appearances in video games, most notable is the Final Fantasy, Castlevania and Devil May Cry series.
Heracles' capturing of Cerberus
Heracles' final labour was to capture Cerberus. After having been set the task, Heracles went to Eleusis to be initiated into the Eleusinian Mysteries so that he could learn how to enter and exit the underworld alive, and in passing absolve himself for killing centaurs. He found the entrance to the underwold at Tanaerum, and Athena and Hermes helped him to traverse the entrance in each direction. He passed Charon thanks to Hermes' insistence, and his own heavy and fierce frowning.
Whilst in the underworld, Heracles freed Theseus but the earth shook when he attempted to liberate Pirithous, so he has to leave him behind. They had been imprisoned by Hades, by magic binding them to a bench, because they had attempted to kidnap Persephone. The magic was so strong that when Heracles pulled Theseus free, part of Theseus' thighs remained on the bench, explaining why his descendants had notably lean thighs.
In some versions, Heracles merely asks Hades for permission to take Cerberus, to which Hades agrees as long as Heracles does not harm the hound, though in other versions Heracles shot Hades with an arrow. In some versions, Heracles drags the dog out of Hades, passing through the cavern Acherusia, but in other versions, Heracles treats the vicious dog with the first kindness it has seen, and easily walks out with it.
Cerberus, Dante's Inferno
In Spanish, cancerbero (from Canis Cerberus, "dog Cerberus") is a Latinate form for gatekeeper, even for a football (soccer) goalkeeper.
Greek Army Emblem with the Cerberus (10th Infantry Brigade / 10 ΤΑΞ ΠΖ) "Guards be aware", a slogan by the Byzantine army guards "the so called Akrites".
Psyche and Cerberus , Edmund Dulac (1882-1953)
Devil May Cry 3: Dante's Awakening, in this game, Cerberus is a boss in the third mission, a metaphor to Dante's Inferno in Canto VI
God of War, a game where some foes are small dogs that, when left undefeated for too long, transform into Cerberus-like creatures.