In myth, it varies, either it was his birthright as the eldest son; or he won that realm in a game of chance (lots, or dice) between his brothers.
After the war with the Titans (the Titanomancy) Zeus, Poseidon, and Pluto divided the world by lots. It just happened by chance that each got his particular domain. . And abducted Persephone
Hades and his brothers were all given areas to rule over. Hades was given the Underworld as his domain.
yes. Poseidon is the god of the sea. Hades is god of the underworld. Zeus is god of the heavens.
Yes he was.. but he was Noble and Fair, unless someone betrayed his trust. newtest3