Nathaniel Adam was a United States Air Force officer during the Vietnam War era. He was framed for a crime he didn't commit and sentenced to death. To avoid execution, he was invited to participate in a military experiment with little chance of survival, with the promise of a presidential pardon should he survive. The experiment involved testing the hull of a crashed alien ship's durability by exploding a super nuclear bomb under it while Adam was in the ship. Against the odds, Adam survived, the alien metal bonded to his skin, which enabled him to absorb and manipulate huge amounts of energy, limited by only his willpower and imagination.

The excess energy of the explosion threw him forward in time nearly twenty years. Everyone had assumed Adam had died during the experiment, so his presidential pardon was never issued and the current government refused to acknowledge the previous administration's promise. Seizing the opportunity at hand, the government used the outstanding murder/treason charges against Adam to blackmail him into being a government-controlled superhero codenamed Captain Atom.

Captain Atom, reluctantly served the government until he succeeded in clearing his name, after which he resigned from the Air Force and found some fulfilment as an actual superhero. Captain Atom joined the Justice League.