Which Titan personified the ocean?

The story behind the answer

Oceanus is correct because he is the Titan who personified the great, earth-encircling river the Greeks believed bordered the world—the source of all seas, rivers, and springs. As a Titan (child of Uranus and Gaia), he’s distinct from later Olympian sea deities.

Context helps separate the options: Proteus is a shape-shifting, prophetic sea god serving Poseidon; Nereus is the gentle “Old Man of the Sea,” father of the Nereids; Pontus is a primordial personification of the sea itself, but not a Titan. Oceanus, with his consort Tethys, fathered the river gods (Potamoi) and Oceanids. Memory tip: “Oceanus = the whole ocean,” the outer boundary of the ancient world.