Definition:

The god Hades, son of Cronus and Rhea, received the Underworld for his realm, when his brother gods, Zeus and Poseidon, received dominion of the sky and sea.

The Cyclops gave Hades the helmet of invisibility to help in the gods' battle with the Titans. Thus, the name Hades means "The Invisible." The realm he rules over is also called Hades.

Hades is the enemy of all life, gods, and men. Since nothing will sway him, he is rarely worshiped.

Sometimes a milder form of Hades, Pluto, is worshiped as the god of wealth, since the wealth of the earth comes from what lies below.

The attributes of Hades include his watchdog Cerberus, the key to the Underworld, and sometimes a cornucopia or a two-pronged pick-axe. The cypress and narcissus are plants sacred to him. Sometimes black sheep were offered to him in sacrifice.

The most familiar myth about Hades is the story of the abduction of Persephone by Hades.

Source: Oskar Seyffert's Dictionary of Classical Antiquities

Examples: As an underworld god, Hades is considered a chthonic deity.