In Greek mythology, Oceanus (/oʊˈsiː.ə.nəs/; Greek: Ὠκεανός, also Ὠγενός, Ὤγενος, or Ὠγήν) was a Titan son of Uranus and Gaia, the husband of his sister the Titan Tethys, and the father of the river gods and the Oceanids, as well as being the great river which encircled the entire world.

When Cronus, the youngest of the Titans, overthrew his father Uranus, thereby becoming the ruler of the cosmos, according to Hesiod, none of the other Titans participated in the attack on Uranus. However, according to the mythographer Apollodorus, all the Titans—except Oceanus—attacked Uranus. Proclus, in his commentary on Plato's Timaeus, quotes several lines of a poem (probably Orphic) which has an angry Oceanus brooding aloud as to whether he should join Cronus and the other Titans in the attack on Uranus. And, according to Proclus, Oceanus did not in fact take part in the attack.

Neptune (Latin: Neptūnus [nɛpˈtuːnʊs]) is the god of freshwater and the sea in Roman religion. He is the counterpart of the Greek god Poseidon. In the Greek-influenced tradition, Neptune is the brother of Jupiter and Pluto; the brothers preside over the realms of Heaven, the earthly world, and the Underworld. Salacia is his wife.

Depictions of Neptune in Roman mosaics, especially those of North Africa, are influenced by Hellenistic conventions. Neptune was likely associated with fresh water springs before the sea. Like Poseidon, Neptune was worshipped by the Romans also as a god of horses, under the name Neptunus Equester, a patron of horse-racing.