Cerberus is the three-headed hound that guards the gates of the underworld, preventing the dead from leaving and the living from entering unbidden [S1][S3][S5]. Son of the monsters Typhon and Echidna (and sibling to the Hydra and the Chimera), he is one of the great 'impossible' creatures of Greek myth [S1][S5]. His capture is the final (twelfth) labor of Heracles, who wrestled him down and brought him to the surface without killing him [S5].