In Greek mythology, Proteus is an early prophetic sea god or god of rivers and oceanic bodies of water, one of several deities whom Homer calls the "Old Man of the Sea". Some who ascribe a specific domain to Proteus call him the god of "elusive sea change", which suggests the changeable nature of the sea or the liquid quality of water. He can foretell the future, but, in a mytheme familiar to several cultures, will change his shape to avoid doing so; he answers only to those who are capable of capturing him. From this feature of Proteus comes the adjective protean, meaning "versatile", "mutable", or "capable of assuming many forms". "Protean" has positive connotations of flexibility, versatility and adaptability.

In Greek mythology, the Nereids or Nereides are sea nymphs, the 50 daughters of the 'Old Man of the Sea' Nereus and the Oceanid Doris, sisters to their brother Nerites. They often accompany Poseidon, the god of the sea, and can be friendly and helpful to sailors.