In Greek Mythology, Cerberus is the three headed dog which guards the entrance to the underworld, also known as the Kingdom of Hades. The dog's role was to prevent the living from entering the land of the dead. There were a few notable exceptions to this, however; Aeneas, for example, drugged Cerberus with a honeycake, and he was lured to sleep with music in another Greek myth. In most depictions of Cerberus, the dog is portrayed as a fierce individual who was so savage that even the Gods were afraid of him.
Descriptions of Cerberus, also known as Kerberos, vary. In most myths, it is agreed that he is the son of Echidna and Typhon, which makes him the sibling of the Lernaean Hydra, the chimera, and several other nasty creatures in the Greek cast of characters. Most stories also depict him with three heads, although poetic license has granted him as many as 100. In some tales, Cerberus has a mane of serpent's heads, and the tail of a serpent.
In one of the more famous myths involving Cerberus, Hercules was ordered to kidnap him from the underworld as his final task in the 12 labors of Hercules. Before embarking on his adventure to the underworld, the Greek hero was initiated in the Eleusinian Mysteries, an Ancient Greek cult which revolved around fertility and the land of the dead. Hercules used his knowledge to find the gateway to the underworld, and he had an assortment of adventures there before kidnapping Cerberus.
Despite being kidnapped, Cerberus apparently remained fierce and awe-inspiring. His venomous saliva sprouted into the deadly plant known as aconite, and he was ultimately returned to Hades to perform his duty as the guard of the underworld. Numerous works of art depict Cerberus in this role, especially in Greek and Roman temples, which sometimes kept dogs to represent Cerberus in the world above.
The “demon of the pit,” as he was known, served as a powerful deterrent to members of the living who were interesting in exploring the underworld in Greek mythology. In the instances where Cerberus was overcome, it often required a trick or a cooperative effort. All Greeks were also aware that they would eventually face Cerberus when they died, as the Kingdom of Hades held all of the dead except for those granted immortality by the Gods.