The ocean, which the Greeks and Romans regarded as a river circling the world. In Greek mythology it was personified as a Titan, son of Uranus and Gaia. In ancient Greek reliefs this Titan is often dipicted as having the upper body of a muscular man with a long beard and horns, and the lower torso of a serpant.
He married his sister Tethys, and from them came the ocean nymphs, also known as the three-thousand Oceanids, and all the rivers of the world.
Some scholars believe he originally represented all bodies of water, including the Mediterranean Sea and the Atlantic Ocean, the two largest bodies the ancient Greeks knew of. However, as geography became more accurate, Oceanus came to represent the stranger, more unknown waters of the Atlantic Ocean while Poseidon ruled over the Mediterranean.
In most variations of the Titanamarchy Oceanus, along with Prometheus, and Themis, did not take the side of the Titans against the Olympians, but instead withdrew from the conflict. In most variations of this myth Oceanus also did not side with Cronus in his revolt against Uranus.