Metamorpho (real name Rex Mason, also called The Element Man) is a fictional character, a superhero in the DC Comics Universe. He is a founding member of the Outsiders, and has also joined multiple incarnations of the Justice League.
Rex Mason was an adventurer who was hired by business tycoon Simon Stagg to retrieve a rare Egyptian artifact, the Orb of Ra. Mason also started dating Stagg's daughter, Sapphire Stagg. This was just one of the incidents that antagonized Simon Stagg.
In an Egyptian pyramid, Rex Mason was knocked out by Simon's brutish bodyguard, Java, and eventually exposed to a radioactive meteorite from which the Orb of Ra was fashioned. A tremendous flare-up of its radiation transformed Rex Mason into Metamorpho, the Element Man. He gained the ability to shapeshift and change himself into any element found in the human body, or any combinations thereof. It was also established in his origin story (The Brave & The Bold #57) that he was virtually invulnerable in his inert (untransformed) state, when Stagg, afraid that Rex was going to kill him, shot him point-blank without effect. The Orb of Ra, however, had the same effect on Rex that kryptonite has on Superman. Thus Stagg continued to control Metamorpho. Later, it was revealed that Mason was but one of many metamorphae, created by the sun god Ra -by this meteor- to serve as warriors in his battle against the god Apep, "the serpent who never dies."