Proteus was a sea-god who could shape-shift
Proteus, a sea god in Greek mythology, had the ability to foretell the future and change his shape at will. He was known for his wisdom and prophetic powers, but he also had a reputation for being elusive and difficult to pin down due to his shape-shifting abilities.
This was Poseidon.
There is the greek god Poseidon, but not many gods in Greek Mythology can actually change forms.
Poseidon is the Greek god of the sea, earthquakes, and horses. He is often depicted with a trident, which he uses to control the seas. As one of the twelve Olympian gods, Poseidon held great power and influence in ancient Greek mythology.
Pretty much all of the gods had the ability to shapeshift.
Well, most gods could ALL change at will, but I'd have to say Posiden, since his grandson could turn into various animals I think, though, that you are looking for Proteus, the shape shifting sea god who was the herder of the sea creatures and called the Old Man of the Sea. He was a prophetic god, but would only give answers if properly compelled to do so, which usually meant clinging to him as he shifted through various forms.
The was the god of the sea and, as "Earth-Shaker," of earthquakes
Proteus in Greek mythology is an early sea god. Proteus is one of several deities in the Old Man of the Sea in whom Homer calls. Some refer to Proteus as the god of elusive sea change.
it isnt a greek god. it is a roman god of sea.
Greek God of the Sea
I think you mean Nereus, but I could be wrong....