Hades, the ruler of the underworld on the nether side of the river Styx was one of the six original Olympian gods. He was the sibling of Zeus, Hera, Poseidon, Hestia and Demeter.
In spite of his Olympian status, Hades rarely left his underworld kingdom. However, he did come into the daylight world to get married. With Zeus's permission, he forcibly abducted the girl Persephone while she was picking flowers in a field.
Her mother Demeter, goddess of the harvest, was deeply upset. She neglected the crops grow and the world descended into winter for the first time. Afterwards, it was only during the girl's annual visits to her mother that plants flourished and bore fruit, only to die down when Persephone returned to spend time with her husband Hades.
The image shows Hades with his three-headed dog, Cerberus, who guarded the gate that led to the underworld, ensuring that the dead were able to arrive but not leave again.
One of the twelve labours of Hercules involved capturing Cerberus without weapons, and bringing him to the surface world. The hero was not able to complete this feat single-handed, however. Other gods helped him.