Pluto (Gr. Ploutōn, from ploutein, 'to be rich'), originally only a surname of Hades, as the giver or possessor of riches, is, in the mythology of Greece, the third son of Cronos and Rhea, and the brother of Zeus and Poseidon. On the tripartite division of the universe he obtained the sovereignty of the under-world—the realm of darkness and ghostly shades, where he sits enthroned as a 'subterranean Zeus'—to use the expression of Homer, and rules the spirits of the dead. His dwelling-place, however, is not far from the surface of the earth. Pluto is inexorable in disposition, not to be moved either by prayers or flatteries. He is borne on a car, drawn by four black steeds, whom he guides with golden reins. His helmet makes him invisible. According to some scholars, his name of Hades is from a priv., and idein, 'to see;' although others, with less probability, derive Hades from hadō or chadō, 'I receive or embrace,' and translate the word the 'all-receiver.' In Homer Hades never means a place, but always a person. Moreover, it is to be noticed that the poet does not divide the realm of the shades into two separate regions. All the souls of the dead—good and bad alike—mingle together. Subsequently, however, when the ethical conception of future retribution became more widely developed, the kingdom of the dead was divided into Elysium (q.v.), the abode of the good, and Tartarus (q.v.), the place of the wicked. This change also exercised an important influence on the conception of Pluto. The ruler of the under-world not only acquired additional power and majesty, but the very idea of his character was essentially modified. He was now regarded as a beneficent deity, who held the keys of the earth in his hand, and possessed its metallic treasures (whence his new name Pluto or Plutus), and who blessed the year with fruits, for out of the darkness underground come all the riches and swelling fullness of the soil. Hence, in later times, mortals prayed to him before proceeding to dig for the wealth hidden in the bowels of the earth.
Pluto married Persephone (Proserpina), the daughter of Demeter (Ceres), after carrying her off from the plains of Enna. He assisted his brothers—according to the mythological story—in their wars against the Titans, and received from the Cyclopes, as a reward for delivering them from Tartarus, the helmet that makes him invisible, which he lent to Hermes (Mercury) in the aforesaid war, to Perseus in his combat with the Gorgons, and which ultimately came to Meriones. The Erinyes and Charon obey his behests. He sits in judgment on every open and secret act, and is assisted by three subordinate judges, Æacus, Minos, and Rhadamanthus. At Elis alone was there a formal cult of Pluto, though in many places in Greece he was worshipped conjointly with Demeter and Korē. Among trees and flowers the cypress, boxwood, narcissus, and maidenhair were sacred to him; black rams and ewes were sacrificed to him amid the shadows of night, and his priests had their brows garlanded with cypress wreaths. In works of art he resembles his brothers Zeus and Poseidon; only his hair hangs down somewhat wildly and fiercely over his brow, and his appearance, though majestic, as becomes so mighty a god, has something gloomy and terrible about it.—The Plutonian theory in Geology, otherwise called Vulcanist or Huttonian, was opposed to the Neptunist or Wernerian. See GEOLOGY, Vol. V. p. 148, and HUTTON; and for the Plutonic rocks, see also IGNEOUS ROCKS.