What was the name of the three headed dog the guarded the underworld?

In Greek mythology, Cerberus or Kerberos 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.
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Cerberus. He guarded the gates of the underworld, allowing the dead to enter but never leave.Chimera was one of Cerberus's siblings as was the Hydra.
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Cerberus. Hades' dog. The original hell hound who guarded hell's gates.Imagine the fights he got into over a bone.Must've been pretty stinkin' vicious...and hillarious.