Hades is the Greek god of the dead. He was the son of Cronus
and Rhea, thus brother of Zeus, Poseidon,
Hera,
Hestia and
Demeter.
Hades constantly lived under the earth in his domain – Tartarus, or Underworld,
or Hell. Hades, the name means 'invisible', was not usually named out loud
for fear of the god; instead euphemisms were used to name him, and one
of such names was
Pluto, which means 'rich', with the hint for vast
richness of the earth.
See: Caravaggio Jupiter,
Neptune and Pluto.