In Greek mythology, Proteus is an early prophetic sea-god whom Homer calls the "Old Man of the Sea" (halios gerôn) — one of several deities who bear that title alongside Nereus and Phorcys. He knows the depths of every sea, foretells the future, and changes shape to avoid being questioned; he answers only those who seize and hold him through every transformation. From this habit comes the English adjective "protean," meaning versatile or mutable.
Adapted from Wikipedia, "Proteus (Greek mythology)" · CC BY-SA 4.0
I.Family
Proteus was often regarded as a son of Poseidon. Later genealogies add a wide range of children: by Torone of Phlegra, Polygonus and Telegonus; by the Nereid Psamathe, Theoclymenus and Theonoe (also called Eidothea or Eurynome); and in other lines Eioneus, Cabeiro, Rhoiteia, Thebe of Egypt, and Thaicrucia.
The Egyptian king Proteus of Euripides' Helen — husband of Psamathe and father of Theoclymenus and Theonoe — is a related but not identical figure in some modern readings: both are tied to Egypt, the sea, and the house of Menelaus, yet the tragic king is already dead when Helen opens, while Homer's immortal Old Man of the Sea still emerges from the waves at Pharos.
II.The Old Man of the Sea
Homer places Proteus on the sandy island of Pharos off the Nile Delta. There Menelaus, becalmed on his voyage home from Troy, learns from Proteus's daughter Eidothea how to ambush her father when he sleeps among his colony of seals at midday. Though Proteus turns into a lion, serpent, leopard, pig, water, and a tree, Menelaus holds him fast until the god speaks truthfully.
Proteus then reveals which god Menelaus has offended, how to appease the gods and sail home, that Agamemnon was murdered on his return, that Ajax the Lesser was shipwrecked and killed, and that Odysseus is detained on Calypso's isle Ogygia — news that reaches Telemachus when the prince visits Menelaus in Sparta.
III.Other myths
In Virgil's Georgics, Aristaeus learns from Cyrene that Proteus can explain why his bees died; compelled in the same way as Menelaus, Proteus reveals the death of Eurydice and the rite of sacrifice from which new bees are born.
Apollodorus reports that Menelaus recovered the real Helen from Proteus in Egypt after Troy had held only a cloud phantom. At Pharos, Hellenistic tradition later associated the site with the Lighthouse of Alexandria.
IV.Cultural legacy
Proteus became a byword for elusive transformation in later literature and philosophy, from Milton and Shakespeare to Jung's use of the figure as a personification of the unconscious. The modern English word "protean" preserves the myth's sense of adaptability.