The grandson of Golden Age villain Cyclotron, Al Rothstein was raised by the original Atom and his wife, and, due to his grandfather's repeated exposure to radiation, grew to over seven feet in height, with an incredibly dense body. He also discovered that he could become immaterial at will or increase his size to over fifteen feet high, and following in his godfather's footsteps, decided to become a crimefighting hero, with the name of Nuklon. He, along with several others, tried to join the original JSA, but was rejected, becoming instead one of the founder members of Infinity Inc. Within this group he came to be close friends with Obsidian, with whom he worked for a number of years, including a brief spell in the Justice League. Recently, Obsidian's darkening personality caused a rift in the pair's friendship, and Nuklon began working alone.
Al has decided to change his codename to Atom Smasher and alter his costume as a homage to both his biological and adoptive families, and soon became involved with the new JSA after Wesley Dodds' funeral, where he has become a big brother figure to the new Star-Spangled Kid. On the team's recent mission, to stop Kobra from committing an internationally significant terrorist act, Al had a personal stake, as Kobra was responsible for the death of his mother, Terri Rothstein, in a plane crash which served as a demonstration of the villain's power. He was extremely tempted to kill Kobra, straining his powers to the limit in the process, but was persuaded not to do so by Jack Knight. A short time later, when the team were faced with what to do about the problem of Extant, Al took the fateful decision to substitute Extant in his mother's place on that plane, saving her and dooming the villain. In the aftermath of this decision, he decided to take some time off from his activities as a JSA member, returning to the team when a mission took them to Thanagar.