Cerberus

Cerberus was the offspring of Typhon and Echidna, two of the most fearsome monsters in Greek mythology. He had three heads (some accounts say fifty or one hundred), a serpent for a tail, and snakes growing from his back. He stood guard at the entrance to the underworld.

The living rarely passed Cerberus. Orpheus lulled him to sleep with his music. The Sibyl of Cumae threw him a drugged honey cake when she guided Aeneas below. Heracles, as his twelfth and final labor, wrestled Cerberus with his bare hands and dragged him to the surface — the only time the hound of Hades left his post.

When Cerberus was brought into the sunlight, he frothed at the mouth, and where his saliva fell on the ground, the poisonous plant aconite (wolfsbane) sprang up. After being shown to King Eurystheus, Cerberus was returned to his post at the gates of the dead.