Proteus

Proteus, the "old man of the sea," tended the seals of Poseidon or Neptune, and had the power of prophecy. This function, however, he was wont to evade the performance of by suddenly changing his shape. Hence the modern proverbial adjective formed from his name. He is variously said to have had his abode in Pharos and Carpathus. Another set of myths makes him a son of Poseidon and a king of Egypt, who receives Helen on her flight thither and restores her to Menelaus.