Dioskilos

Dioskilos is an antagonist in the 1981 movie Clash of the Titans. It is a two-headed dog from the Underworld who protects Medusa's hideout and kills the intruders.

History
After being carried to the Underworld by Charon, Perseus and three soldiers go to the temple of Medusa. However, Perseus accidentally drops a statue and Dioskilos hears them. Perseus and one of the soldiers pass near the den of Dioskilos, who suddenly pounces on them and kills the soldier. Dioskilos attacks Perseus and disarms him, but the two other soldiers come and fight the two-headed monster. Perseus recovers his sword, then he joins the fight and manages to stab one of the heads. He injures the other head and makes Dioskilos fall from a wall before jumping on it and throwing it a fatal blow.