Nereis, a marine divinity in Greek and Roman mythology, son of Pontus and Gaea (or, in the Roman myth, of Oceanus and Terra), and husband of Doris, who bore him 50 daughters, the Nereids. Nereus was represented as a benevolent, wise, and gentle old man, one of the most unerring prophets among the minor divinities. He dwelt at the bottom of the sea (according to most authors, of the Aegean sea, over which he especially ruled). His attribute was the trident, and he frequently appears in ancient works of art. - The Nereids were the nvmphs of the Mediterranean, as the Naiads were of the fresh water, and the Oceanides of the outer ocean. Their individual names are given by several authors, but are not always the same in different passages. They were represented as beautiful girls, generally grouped about the ears of marine divinities, or in dances or revels with tritons and monsters; sometimes they are represented as mermaids. They were thought to be especially propitious to sailors, and were widely worshipped in the Greek seaports.

Perhaps the most celebrated of the Nereids was Thetis, the wife of Peleus and mother of Achilles.