In the Twelve Labors of Hercules, Hades was the master of Cerberus.
Cerberus served as the watchdog of the underworld, the realm ruled by Hades. His role was to prevent the dead from leaving and the living from entering without authorization. For Hercules’s final labor, Eurystheus demanded that the hero bring Cerberus to the surface alive. Hercules therefore had to obtain permission from the underworld’s rulers before subduing the creature.
Hades is sometimes confused with the name of the underworld itself, but in Greek mythology Hades is both the god and the ruler of that realm. Cerberus’s parentage is usually given as Typhon and Echidna. The dog’s number of heads varies across artistic and literary traditions, although three heads became the standard popular image.