Ultra the Multi-Alien is a composite creature with one quarter of its body composed of each of four alien races. The name ULTRA is also a composite, with a letter from each of the four monsters plus A from Ace Arn.
While piloting a tourist space cruise, pilot Ace Arn's ship was caught in the magnetic field of a comet. After evacuating the ship, Arn was himself unable to escape, slipping into suspended animation and being carried to another solar system by the comet's intergalactic orbit.
Eventually, his ship crash landed on an asteroid and Arn awoke in an underground cavern, the headquarters of a now deceased alien named Zobra.
Zobra had invented a weapon which would transform whomever it was fired at into a duplicate of the being firing the weapon. Each of Zobra's four lieutenants, from four different alien worlds, was armed with one. At precisely the same moment, all four fired at Arn, with the result being Arn's transformation into a conglomeration of the four aliens. Using the powers he gained from this transformation, Arn defeated the four, and after repairing his spaceship, ventured to Earth.
Arn, now having taken the name Ultra, found that he could not transform back to his humanoid form and devoted much of his time to finding a cure for his transformation. During a battle with Doctor Dynamo, Ultra discovered that the villain's Demoleculizer could restore his true form.
However, when he had to regain his Ultra form to defeat Dynamo, the villain destroyed the Demoleculizer, again trapping Arn in his alien form. Further attempts to effect change eventually proved successful (though not without mishaps on the way) and Arn built a hyper-converter disc which enabled him to alter his form without any trouble.
Ultra is a future era character but in recent appearances this has been ignored and he has shown up in contemporary DC events.
It was discovered that Ultra was abducted by Brainiac at some unknown time. He was in stasis aboard Brainiac's ship along with the Creature Commandos. Brainiac eventually triggers their release while activating his robots to kill Superman and the Kryptonians. Everyone in the ship fights off the attack. While the Creature Commandos, having been launched into space in the 1940's, had no idea who Superman was, Ultra, referring to his life in the future, recognizes him.
Ultra as reappear as an infant, result of the experimentation made by Byth, with the fusion of dna from differentt species, human included. Byth also called him "Slayer of worlds".