Okeanos is the eldest of his eleven other siblings.
He rules all if the odd bodies of water (not the Mediterranean Sea, that’s Poseidon’s domain. We’ll get to that later). At some point, Okeanos married his sister Tethys. They had many children called the Oceanids. Tethys and Okeanos had so many children that it began to flood so the two siblings had to divorce to prevent it from happening again.