Hades (ˈheɪdiːz; Háidēs, ˈhaiː.dεːs or ˈha.dεːs), in the ancient Greek religion and mythology, is the god of the dead and the king of the underworld, with which his name became synonymous. Hades was the eldest son of Cronus and Rhea, although this also made him the last son to be regurgitated by his father. He and his brothers, Zeus and Poseidon, defeated their father's generation of gods, the Titans, and claimed rulership over the cosmos. Hades received the underworld, Zeus the sky, and Poseidon the sea, with the solid earth, long the province of Gaia, available to all three concurrently. In artistic depictions, Hades is typically portrayed holding a bident and wearing his helm with Cerberus, the three-headed guard dog of the underworld, standing to his side.
The Etruscan god Aita and the Roman gods Dis Pater and Orcus were eventually taken as equivalent to Hades and merged into Pluto, a Latinisation of Plouton (Ploútōn), itself a euphemistic title often given to Hades.
The origin of Hades' name is uncertain but has generally been seen as meaning "the unseen one" since antiquity. An extensive section of Plato's dialogue Cratylus is devoted to the etymology of the god's name, in which Socrates is arguing for a folk etymology not from "unseen" but from "his knowledge (eidenai) of all noble things". Modern linguists have proposed the Proto-Greek form *Awides ("unseen"). The earliest attested form is Aḯdēs (Ἀΐδης), which lacks the proposed digamma. Martin Litchfield West argues instead for an original meaning of "the one who presides over meeting up" from the universality of death.
In Homeric and Ionic Greek, he was known as Áïdēs. Other poetic variations of the name include Aïdōneús (Ἀϊδωνεύς) and the inflected forms Áïdos (Ἄϊδος, gen.), Áïdi (Ἄϊδι, dat.), and Áïda (Ἄϊδα, acc.), whose reconstructed nominative case *Áïs (*Ἄϊς) is, however, not attested. The name as it came to be known in classical times was Háidēs (Ἅιδης). Later the iota became silent, then a subscript marking (ᾍδης), and finally omitted entirely (Άδης).