In Greek mythology, Cerberus was the three-headed dog guarding the entrance to Hades.
Cerberus prevented the dead from leaving the underworld and kept living visitors from entering without permission. He was usually described as the offspring of the monstrous pair Typhon and Echidna. Although later images often emphasize three heads, ancient descriptions vary in details such as the number of heads, serpent features, and the creature’s tail.
Capturing Cerberus was the final labor of Heracles. The hero brought the dog to the world above under conditions that differed among ancient accounts, then returned him to Hades. The labor demonstrated Heracles’ strength while also marking a journey into a realm normally closed to mortals.
Cerberus is often confused with Orthrus, another two-headed dog in Greek myth. Orthrus guarded the cattle of Geryon and was also a child of Typhon and Echidna, but he was not the guardian of Hades.