In Greek mythology, Cerberus or Kerberos (Greek Κέρβερος, Kerberos, "demon of the pit") was the hound of Hades, a monstrous three-headed dog (sometimes said to have 50 or 100 heads) called a hellhound. Cerberus guarded the gate to Hades and ensured that spirits of the dead could enter, but none could exit (additionally, no living person was to come into Hades). Among his siblings are Chimera and the Hydra. He is the offspring of Echidna and Typhon.
In the Greek Oracle of the Dead at Cumae in southern Italy, the recently excavated subterranean shrine was found to contain chains fixed to the wall for three large dogs before the entrance to the shrine of Hades and Persephone. The three dogs would have represented Cerberus in this ancient temple.
In the last of his Twelve Labours, Hercules was to capture Cerberus. After having been given the task, Hercules went to Eleusis to be initiated in 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 underworld at Tanaerum, and Athena and Hermes helped him to traverse the entrance in each direction. He passed Charon with Hermes's assistance and his own heavy and fierce frowning.
Whilst in the underworld, Hercules freed Theseus, but the earth shook when he attempted to liberate Pirithous, so he had to leave him behind.
They had been imprisoned by Hades, by magically binding them to a bench, because they had attempted to kidnap Persephone. The magic was so strong that when Hercules pulled Theseus free, part of Theseus's thighs remained on the bench, explaining why his descendants had notably lean thighs.
Hercules presented himself before the throne of Hades and Persephone and asked permission to take Cerberus, to which the gods agreed as long as Hercules did not harm the hound in any way. Some say Persephone gave her consent because Hercules was her own brother. In any case, Hercules wrestled the dog into submission and dragged it out of Hades, passing through a cavern entrance in the Peloponnkse. When he returned with Cerberus to the palace, Eurystheus, the man who had assigned the task to Hercules, was so afraid of the fearsome beast that he jumped into a pithos (large storage jar) to hide. From the spittle of the dog which fell upon earth, the first poisonous plants were born, including deadly aconite.
I.Nemean Lion II.Lernaean Hydra III.Ceryneian Hind IV.Erymanthian Boar V.Augean Stables VI.Stymphalian birds VII.Cretan Bull VIII.Mares of Diomedes IX.Girdle of Hippolyte X.Cows of Geryon XI.Apples of the Hesperides XII.Cerberus