Anti-matter Man is a fictional cosmic entity of the DC Comics universe. He first appeared in Justice League of America # 46 (October 1966).
Anti-Matter Man Wikipedia
No one knows the origin of the Anti-matter man but he seems to be an explorer from the antimatter universe of Qward. He appears as a gigantic slim blue man wearing orange clothing. He bears a passing resemblance to Repello-Man, a creature created on the orders of the Earth-One Johnny Thunder, a villain from the previous Crisis story. He was ignorant or unconcerned about his effect on the positive matter Universes. When he came, the parallel worlds known as Earth 1 and Earth 2 began to merge in Warp space, due to a scientist on Earth-1 working on a sub-space machine. The result is that many persons from these dimensions have been transported one to another. The Batman of Earth 1 and Blockbuster went to Earth 2, Dr. Midnight and Solomon Grundy came on Earth 1. For the heroes, the primary threat seemed to be the two villains. But the Spectre with his higher consciousness, felt the advance of Antimatter Man on Earth 1 and 2 by travelling through warp space, and that he should be responsible for that confusion. Moreover, he sensed that the mere presence of that being in any of the lands would mean immediate annihilation. The Spectre tried to stop their advance, but the properties of the mysterious antimatter body was affecting its structure, when Spectre tried punching him, his arm had shrunk. When the creature returned the punch, the head of Spectre inflated like a balloon. His legs then shrunk down from another blow.
Stunned, the Spectre noted that the Earths 1 and 2 were merging, even if the Man of antimatter not stepped there, those worlds were already condemned. In an almost metaphorical act, the Spectre stands between an Earth and another, pushing them and trying to avoid that they are merged. But his power was only sufficient to slow the process, and he was weakening as Anti-Matter man got closer. Desperate, our hero sends a message to Dr. Fate, who calls the Justice League and Justice Society to stop the threat. Dr. Fate brings together groups within portal where the plot unfolds. It covers their bodies with magic, so they do not explode on contact with the Antimatter Man, and casts a spell that creates a breathable atmosphere on the site (remembering that Spectre is a spiritual being, and does not need to breathe). Dr. Fate also creates a mystical ring around of the Antimatter Man, to slow its advance. The superheroes attacked Anti-Matter Man, but he was able to turn back their powers and warp them, such as making a cage around Doctor Fate with his magic, making Black Canary's hair grow so long it passed her feet, and sticking Batman and Wildcat together back to back. But despite these the heroes were able to stun Anti-Matter Man and drag him away from the Earths. Doctor Fate realized Anti-Matter Man was an explorer from the Anti-Matter Universe, and regarded what had happened to him as odd hazards of Warp-Space he must overcome to reach his destination. However he was then revived, but the Atom, who was in the same Lab as the machine that was causing the Earths to merge, saw the Spectre in the screen of the machine and transported himself into Warp-Space. He told the Spectre how to separate the Earths, he must shrink to an inch in height, then suddenly grow and cause an explosion that would blow the Earths apart, though he would probably be destroyed. The Spectre agreed to this, and the Atom helped him. After the Earths had been forced apart the Spectre reformed, revealing he had placed an electromagnetic field round his body to reform it. The waves of the explosion forced Anti-Matter Man back into his Universe, but it is unknown if he will return.
The powers of the Anti-Matter Man were very strange and unpredictable. Because of his antimatter body he could not touch positive material from our universe, at the risk of causing explosions. However the magic of Dr Fate can protect people from this effect. Anti-Matter Man was massive in size, at tens of meters long. When fighting magical or ethereal creatures as the Spectre, Antimatter Man has the advantage because magic from our universe is not as effective against him. He could even warp the Spectre's body by touching him, and his presence weakened the Spectre. However he is vulnerable to impact blows. He can control organic and inorganic matter at will, and even reverse their powers against him, even Green Lantern energy and Dr Fate's magic.