It is no exaggeration to say that the advent of the nuclear age changed the world as we knew it, and the world of comics echoed that sense of wonder and uncertainty. Initially, the atomic bomb was seen as a positive development, at least as far as the war effort was concerned, and comics were quick to exploit this (in fact, some even speculate that Burtis Publishing's Atomic Bomb #1 pre-dates the Hiroshima bomb). The first significant atomic superhero was Atomic Man, who debuted in a 1943 issue of Prize Publishing's Headline Comics. Atomic Man dispatched underworld hoods with a quick zap of his fingers, but it could be argued that his most notable features were his peculiarly Aztec-style helmet and the fact that he wore a skirt. Atomic Man was not, however, unique: Other titles such as Atoman,Atomic Thunderbolt, and two separate Atomic Comics appeared in 1946.
Even at this early date there was ambivalence and uncertainty about the bomb. On one side there were broadly positive atomic stories in strips as diverse as those of Superman, the Shadow, Midnight, Robin, Superduck (in which the cantankerous mallard makes his own A-bomb) and Pyroman, who was shown on the cover of Startling Comics #41 jubilantly hugging his own atom bomb. On the other hand, the horror and anxiety resulting from the devastation caused in Hiroshima and Nagasaki were reflected in a 1946 Captain Marvel story in which all manner of countries nuke each other into oblivion, leaving the Captain the last man alive on the planet. But this was only an imaginary story, so that's all right, then.