Cerberus

Cerberus was a Greek beast.

Mythology
Cerberus was a three-headed dog that guarded the gates of the Underworld. He prevented the ghosts of the deceased from leaving the Underworld, rather than preventing others from getting into the Underworld. He was sometimes depicted as having a mane of serpents and a serpentine tail. As one of his labors, Heracles had to capture the beast, which he did with the help of Persephone.

Relationships

 * Parents: Typhon and Echidna