Kerberos — Greek mythology

Kerberos, the Three-Headed Dog
Roman name: Cerberus
Today, many people refer to the ancient Greek deity Kerberos by his Roman name, Cerberus. Whether you call him Kerberos or Cerberus, he was the three-headed dog who guarded the gates to the Underworld, home of the powerful god, Hades.
Hades loved that fierce, bad tempered dog. Sometimes, just for fun, Hades and his beloved dog Cerberus would climb aboard Hades' golden chariot and tear across the Underworld, scattering the souls of the dead, who had to dive left and right to get out of their way.

But mostly, Cerberus guarded the gates, making sure no one entered or left without permission. Orpheus managed to sneak into the Underworld by lulling Cerberus to sleep with his beautiful music. But that only happened once. Cerberus was a very good watchdog.

Family
According to Hesiod, Cerberus was the second of the four monstrous children of Typhon and Echidna, being born after Orthus, the two-headed hound who guarded the cattle of Geryon, but before the Lernaean Hydra and, quite possibly, the Chimaera – all of them multi-headed. Later authors list many other monsters among the siblings of Cerberus, including the Sphinx, the Nemean Lion, the Caucasian Eagle, the Crommyonian Sow, the Colchian Dragon, Ladon, and even Scylla and the mother of the Gorgons. Quite a family, indeed!

Portrayal
As to the number of Cerberus’ heads we have contradictory testimonies. Hesiod, for example – after pointing out that Cerberus’ monstrosity was almost indescribable – also adds that he, “the brazen-voiced hound of Hades,” is “fifty-headed, relentless and strong” creature who feeds on raw flesh. Pindar goes a step further, claiming that Cerberus has twice more, i.e., one hundred heads.

However, possibly due to practical reasons, in art he is almost exclusively shown with three heads, and sometimes even with two or just one. Later authors, trying to reconcile the descriptions, started claiming that Cerberus had three dog heads, the rest of them being the heads of snakes spurting from his back, with a venomous one also serving as his tail.