A trained, dedicated soldier Allen Adam was working on an experimental rocket and he was accidentally launched into space. As he entered the upper atmosphere, the rocket exploded and Allen was atomized. However, he gained atomic abilities and was able to reform his body when he returned to the ground. Also, his hair would turn white when he transformed. He outfitted a red and yellow costume for himself and he became Captain Atom.
In the months that follow, Captain Atom protected America against alien invasions and a variety of supervillains, until he was forced to extend himself to the limit to shut down a nuclear reactor gone wild. He then found that the encounter had left him powerless. He was then captured by the renegade scientist who had tampered with the reactor, and was unmasked on nationwide television.
Adam eventually regained his powers and escaped his captor. However, his radiation levels were becoming more and more unstable, which Adam allowed himself to be coated in an experimental new liquid metal, a formula that was absorbed under his skin and was absolutely radiation-proof. Triggered by a power surge in his body, the metal covering would become visible, revealing Adam's new costume, while containing his excessive radiation.
In his later adventures, Captain Atom often worked with superheroine Nightshade.
Adam and his fellow heroes helped fight the Anti-Monitor and his minions during the Crisis on Infinite Earths. Following the Crisis, Adam helped Superman and Firestorm on a mission before he was erased from existence, replaced by the New Earth version of Captain Atom.
- Atomized Physiology
- Flight: 20000 miles per hour to 100000 miles per hour.
- Atomic Blasts
- Superhuman Strength
- Superhuman Durability: He can survive to 10000°C.
- Invisibility: by manipulating the light around him, he can become invisible.
- Atomic Explosions: Captain Atom can release a 100 megaton-level explosion.
- Enhanced Sense of Smell: He can smell nitroglycerin in almost zero-gravity places. 
- Enhanced Vision
- Enhanced Senses: Captain Atom can sense the presence of living beings by the heat of their bodies. He can also sense the presence of radiation.
- Self-Sustenance: Captain Atom can survive without air and food.
- Molecular Reconstruction: Captain Atom has low degree of transmutation.
- Force Field
- Power Loss: Both Captain Atom and Firestorm's powers become neutralized when they are near each other.
- This version of Captain Atom, including all history and corresponding appearances, was erased from existence following the collapse of the original Multiverse in the 1985–86 Crisis on Infinite Earths limited series. Even though versions of the character may have since appeared, this information does not apply to those versions.
- On several occasions, Adam's surname was spelled "Adams", even when in the same story, it's also spelled Adam. Several adaptations of the post-Crisis Captain Atom changed the name to Adams as well.
- Allen Adam's first name also changes. In Charlton Bullseye (Volume 2) #7, it is "John". In Who's Who: The Definitive Directory of the DC Universe #4, Convergence: Blue Beetle #1 and a few other places, it is "Nathaniel", the same as his Post-Crisis counterpart. However, "Allen" is the most common and earliest version.
- Captain Atom's pre-Crisis origin would be modified and used as the government's "official origin" of the post-Crisis Captain Atom as a cover-up.
- 50 Appearances of Allen Adam (Earth-Four)
- 14 Images featuring Allen Adam (Earth-Four)
- Quotations by or about Allen Adam (Earth-Four)
- Character Gallery: Allen Adam (Earth-Four)