In Greek mythology, Proteus (/ˈproʊtiəs, -tjuːs/; Ancient Greek: Πρωτεύς) 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” (halios gerôn). Some who ascribe to him a specific domain call him the god of “elusive sea change”, which suggests the constantly changing nature of the sea or the liquid quality of water in general. He can foretell the future, but, in a mytheme familiar to several cultures, will change his shape to avoid having to; he will answer only to someone who is capable of capturing the beast. From this feature of Proteus comes the adjective protean, with the general meaning of “versatile”, “mutable”, “capable of assuming many forms”. “Protean” has positive connotations of flexibility, versatility and adaptability.
Source: Proteus – Wikipedia