Greek & Roman Mythology
Hades is the god of the Underworld and with his three-headed dog Cerberus who guards the gates to prevent the dead from leaving. He is married to Persephone (daughter of the goddess Demeter), depending on which version, where Persephone found a way into the Underworld and wanted to stay or was kidnapped, but regardless both grew to love each and Persephone became queen of the Underworld. He is the older brother or Zeus and Poseidon, and the eldest of the sons of the Titan Cronos.
His Roman counterpart is Pluto.
In the New 52, Hades appears to be but a child with pasty white skin, a dark suit of armor and most unusually a number of candles where the melted wax obscures most of his face above the nose. As a more modern name for himself he told Lennox to call him Hell.
He is still the ruler of the underworld and the dead, but it appears deeper than it first sounds, more that the reason his realm carries his own name is because he literally is his own realm and everything in it is an extension of his will.
Despite being seen as an evil character in several media, there isn't much to suggest that he's evil, in comparison, Hades is the more far and just gods in Greek Mythology. When individuals came to him in their time of need, he choice not to turn them away, but instead gave them the chance to earn what they desire. He is not against helping those in need, but only if they can prove themselves worthy.