Oceanus was the primordial river or divine personification believed by the Greeks to encircle the inhabited world. He belongs to early cosmological traditions in which seas, rivers and divine genealogies explain the structure of the universe.
In Hesiodic genealogy Oceanus and Tethys are parents of the river gods and Oceanids, linking the primordial deity to the waters that organise the mythical cosmos. Unlike the younger Olympians, Oceanus rarely appears as an active participant in heroic narratives. His importance is chiefly cosmological, preserving an early Greek conception of a world surrounded and sustained by a great encircling stream.
In Homer’s The Iliad, Oceanus is the primordial river-god imagined as encircling the world and belongs to the divine cosmology invoked by gods and mortals throughout the poem. The Odyssey uses Oceanus as a geographical and mythic boundary at the edge of the known world, especially in Odysseus’s journey towards the land of the dead, where the hero’s travels pass from ordinary seafaring into a landscape defined by cosmic geography.