Cyclotron was an atomic scientist in the 1930s and 1940s named Terry Curtis (born Terrence Kurtzenberg, he had later Anglicized his name). In the past, he had had a brief romantic relationship with Dannette Reilly, the second Firebrand. Curtis was eventually kidnapped by the villainous Ultra-Humanite who sought to make use of the scientist's expertise with atomic energy. He was subjected to the Humanite's experiments and exposed to radiation which granted him superhuman abilities.
Used as a pawn by the villain, Curtis was forced to go up against the heroic All-Star Squadron. In the process, he waged battle with the original Atom, exposing the hero to powerful radiation. This later became the source of the Atom's own superhuman abilities. Cyclotron died trying to be a hero by taking the Humanite into the atmosphere and allowing himself to blow up. Inspired by this selfless sacrifice (and the super-power left in its wake), the Atom would later adopt a costume patterned after Cyclotron's own.
Curtis' daughter, similarly named Terri, entered the custody of Firebrand and the Atom. The two served as godparents to Terri's baby, with Curtis' ex-lover Firebrand raising the child herself. Though cured of any potential radiation poisoning, Terri had evidently absorbed a large dose of her father's energy and passed the side-effects to her son Albert who became the hero Nuklon (later Atom Smasher).