Ray Palmer, at Ivy University, uses the properties of a white dwarf star to shrink himself to many different diminutive sizes, down to the sub-atomic scale (first appearance, Showcase No. 34, Sep/Oct 1961: "Birth of the Atom"). After mastering this ability, Palmer calls himself the Atom and joins the fight against crime. The Atom has many adventures with Superman as both are members of the Justice League of America.
Jor-El sends a tape to Earth that shows simulated future outcomes, one of which recounts Superman becoming a hero that has the look and powers of the Atom (Act No. 314, Jul 1964: "The Day Superman Became the Flash!"). In another tale, Superman and the Atom are stranded in a sub-atomic world and help rescue it from a threatening entity (WF No. 213, Aug/Sep 1972: "Peril in a Very Small Place!"). With the Atom, Superman also battles Sabronian villains who intend to wreck the Fortress of Solitude (DCCP No. 15, Nov 1979: "Plight of the Giant Atom!").