Rex Mason was a bold adventurer, globetrotter, and soldier of fortune, in the style of heroes who populated the pages of old pulp novels. One day, Mason was hired by billionaire Simon Stagg, the CEO of Stagg Industries, to find and bring back a rare and ancient Egyptian treasure known as the Orb of Ra. However, not long after contracting him for the job, Simon Stagg discovers that Mason has been dating his daughter, the bombshell beauty Sapphire Stagg. Because of Mason's rather large personality, Simon Stagg thought he would usurp his status as the most important person in his daughter's life, causing an irrational hatred for Mason. All of this resulted in an elaborate plot from Simon Stagg to eliminate Rex Mason for good.
While inside the Egyptian pyramid where the Orb of Ra is said to be residing, Mason is knocked unconscious by Simon Stagg's Neanderthal-like bodyguard named Java. Now trapped in the pyramid, he finds himself exposed to the energies of the radioactive meteorite from which the Orb of Ra was created from, known as the meteor of Ahk-Ton. The energy of the meteor changes him physically, and Mason soon finds out the he now has the power to shapeshift and change himself into any combination of elements found within the human body. He also discovers that he is practically invulnerable when he is in an inert and unmoving state. However, his face is now pasty white and disfigured, and the rest of his physical body becomes segmented, with each limb appearing to be entirely made of a different elemental substance.
Simon Stagg becomes terrified of the new creature he has inadvertently created, and attempts to shoot him and kill him, but to no effect. But The Orb of Ra itself turns out to be Mason's only weakness, and he is crippled whenever he is in its presence. Simon Stagg then used the Orb to control him. He feigns guilt over what happened to Mason, and promises to try and find him a cure. Now calling himself Metamorpho, the Element Man, Mason embarks on a career as a Super-Hero.
Despite his monstrous appearance, Sapphire Stagg does not reject Mason, and her father Simon uneasily accepts that his daughter and the freak he helped create enter into a long and passionate romantic relationship. Regardless of her acceptance, Rex Mason sees himself as a monster, because he cannot transform back into his original appearance, and does everything he can to find a cure himself, but is unsuccessful. He seeks the Justice League of America's help in reversing his condition, but they find themselves unable to help him. They offer him membership, but he refuses, instead accepting his status as a JLA reservist.
During these early years, Metamorpho briefly takes on a crimefighting partner named Urania "Rainie" Blackwell, who called herself the Element Girl. She deliberately exposed herself to the Orb in an effort to gain powers identical to that of Metamorpho. She ultimately stops working with Mason however, because she is madly in love with him, and he only has eyes for Sapphire Stagg. Rex spent the next several years trying to cure himself, but to no avail. He teamed up several times with the Batman during this era, and forever gained the Dark Knight's respect.
After many years of solo adventuring, as well as occasionally helping the Justice League, Metamorpho went to the small European country of Markovia to seek the help of its leading scientist, Dr. Helga Jace, in removing his powers. It was while he was in Markovia that the villainous Baron Bedlam attempted to stage a coup. Metamorpho joined with other heroes, some new and some established, all under the leadership of the Batman, in an effort to free Markovia, and a new super team was formed. Rex dubbed them the Outsiders, and the name stuck. This new team would be Metamorpho's surrogate family for several years.
While working on finding a cure for Mason, Dr. Jace reconnected Metamorpho with his longtime girlfriend Sapphire Stagg. The reunion was short-lived however, as her father Simon decided to kill Metamorpho once and for all using the Orb of Ra. Seeking a way to revive Metamorpho, she convinces the Outsiders her return to Egypt, to help her look for the original meteor of Ahk-Ton. When they are accidently sent back in time to 1200 B.C., Metamorpho's body was exposed to the ancient meteor all over again and was restored to life. But as soon as he returned to his own time, he found out that this second exposure has trapped him in the form of Metamorpho permanently. However, Sapphire Stagg proposed marriage to him regardless of his permanent, to which Rex readily said yes.
Despite all of Dr. Jace's help, it was revealed she was a sleeper agent for an ancient organization known as the Manhunters. She killed Metamorpho, as well as herself in the process. Rex was considered dead for months, until the alien invasion of the race called the Dominators occurred. When the alien race activated their so-called "gene bomb," meant to activate the metahuman gene in humans, Metamorpho was awakened, and returned from the grave.
Rex had temporary amnesia of many events towards the end of his life, and he forgot reconnecting with and marrying Sapphire. He moved to France to become a charter member of Justice League Europe, and after several adventures with the team, his wife came looking for him, and dropped a bombshell on him -- he had an infant son named Joey. After his "death" however, Sapphire was pressured by her father Simon into marrying his bodyguard, and Rex saw this as an absolute betrayal, ending any chance for a reconciliation.
Staying with the JLE, Rex then fell for his new Justice League teammate Vivian D'Aramis, also known as the Crimson Fox. But that relationship was also not meant to last. Not long after, Metamorpho discovered that his son Joey was born cursed with similar powers, and transformed anything he touched. But when he came in contact with the meteor of Ahk-Ton, their energies cancelled each other out, and Joey Mason was rendered normal.
When the Justice League International lost their UN charter, they reformed as an independent League located out of a satellite in space. During an alien incursion, Metamorpho found himself struck by a powerful energy blast that destroyed his body. However, he reforms into a new body, one which looks significantly different from his original one. When the League's satellite HQ is attacked, Metamorpho uses his body to save his fellow Leaguers upon reentry from space. He was rendered inert, and although not officially dead, he ends up buried in Valhalla Cemetery, the Super-Hero graveyard.
Metamorpho returns once again, after an all-powerful sixth-dimensional being comes to Earth and granted everyone's desires. Rex's son Joey Mason wished for his father to be brought back to life, and for a time, he was. But once the imp was defeated, Rex Mason returned to being dead. But while Mason's body lied inert in the ground, his spirit contacted his former wife Sapphire, and she used the Orb of Ra to truly restore Metamorpho to life for real. Not long after, he joined the short-lived corporately sponsored incarnation of the Doom Patrol.
Some time later, a somewhat different looking version of Metamorpho joined Nightwing's new incarnation of the Outsiders. But things were not as they seemed, as this was an aspect of Rex Mason that had been split off from him when he saved the JLA years earlier upon reentry into Earth's atmosphere. A piece of Rex had broken off, and equipped with most of his memories, thought itself to be the real Rex. After joining these new Outsiders, the real Rex arrived and revealed the truth to him, and asked him to rejoin him and merge. But Nightwing insisted that he had become a separate lifeform, and deserved a chance to live. He stayed with the Outsiders under the new name "Shift."
After some time however, Shift chose to be assimilated into Metamorpho of his own free will, because he had accidentally killed forty four people while on a mission, and couldn't live with the guilt of what he'd done. Afterwards, Metamorpho took over Shift's role in the Outsiders. When Batman took over the team once again, Metamorpho stayed on. He was apparently killed when Talia al'Ghul destroyed a satellite the team was on, but it was later revealed he had used his powers to save himself and his friends.
Although largely absent from the DC Universe after it was altered by the events of 2011's FLASHPOINT, Rex Mason reemerges during the Rebirth era. Simon Stagg forces Rex to change himself into Nth Metal as part of an attempt to open a portal to the Dark Multiverse. Later, Metamorpho would team up with Mister Terrific and Plastic Man in an effort to close the portal before the Dark Multiverse could overrun ours. When they manage to leave the Dark Multiverse behind, Rex alongside these other heroes form The Terrifics.