The Greek titan Oceanus (also spelled Okeanos) was the son of Uranus and Gaia. The ancient Greeks considered him the god of a river that encircled the world and that was the source of all the fresh water on earth (for them, the world was a flat disk surrounded by water). Later, as geography developed, Oceanus referred only to the Atlantic and Indian Ocean.
He was represented as having a beard and horns on his forehead (sometimes in the shape of crab claws). The lower part of the body was snake-like or was a fish tail.
Together with Prometheus and Themis, he didn't take part in the war between Titans and Olympians.
The Greek titan Oceanus was also the god who took care of the rising and setting of the celestial bodies. They would emerge from his waters, travel across the sky and descend again into the ocean.
Helios, for instance, would rise in the East; after his journey across the earth, he would descend in the West and then, through the ocean, he would return back to East during the night. In Deipnosophistae, the author, Athenaeus of Naucratis, tells us that at the end of the day Helios climbs into a golden cup, in the Hesperides land, in the West, and sails with it to the land of the Ethiops, in the East.
By the way, all the things that were strange and mysterious were said to be situated by the Ocean (the garden of the Hesperides, the mysterious island Leuke).
His wife was Thetys, and together they had thousands of daughters and sons: 3,000 Oceanids (nymphs of all the lakes, ponds, springs, rivers, seas) and 3,000 Potamoi (river-gods). The Greek titan Oceanus and his wife also took care of Hera when she was little.
This is one of the most famous representations of Oceanus, even if it is better known as "Bocca della verità" (The mouth of truth). And please don't tell me that you don't know it, at least from the famous scene in the movie Roman Holiday!