A native of the planet Braal (although his parents were on Earth at the time he was born), Cosmic Boy possesses, like all the inhabitants of his planet, the "power of super-magnetism," the ability to release powerful magnetic emanations from any part of his body. Cosmic Boyâ€™s real name is Rokk Krinn. He continues in the Adult Legion of Super-Heroes as Cosmic Man.
In August 1961 Cosmic Man and two other adult Legionnaires—Lightning Man and Saturn Woman—join forces with Superman in his battle with Lex Luthor and the Legion of Super-Villains (S No. 147/3: "The Legion of Super-Villains!").
In April 1962 Cosmic Boy is among the six Legionnaires who play an elaborate hoax on Superman and Supergirl as a prelude to celebrating the anniversary of Supergirlâ€™s arrival on Earth (S No. 152/1: "The Robot Master!").
In August 1962, Cosmic Man and Lightning Man pose as Hercules and Samson, "two of the mightiest men of all time," as part of an elaborate ruse, devised by Superman, for uncovering the hiding place of Duke Marple's stolen loot and bringing the "notorious gang-leader" to justice (S No. 155/2: "The Downfall of Superman!").
In October 1962, when Superman is believed to be dying of an incurable malady, Cosmic Boy is among the Legionnaires who are summoned to the twentieth century by Supergirl to help carry out the gigantic super-tasks that Superman hopes to fulfill as his final legacy to humanity, including the destruction of a "vast cloud of fungus in distant space, that will some day reach Earth and blight all plant life," and the melting of the Antarctic ice, "to make Antarctica a fit place for millions to live in the future," thus ensuring "a home for Earthâ€™s expanding population...!" (S No. 156: "The Last Days of Superman!" pts. I-III—"Superman's Death Sentence!"; "The Super-Comrades of All Time!"; "Superman's Last Day of Life!").
In October 1964, after Superman has been deprived of his super-powers by the baleful radiations of a mysterious green comet, Cosmic Boy and two of his fellow Legionnaires—Saturn Girl and Invisible Kid—use a "time-force wave carrier" in their thirtieth-century clubhouse to endow Superman temporarily with their various powers so that he can use them in his upcoming battle with Lex Luthor and Brainiac. For a period of "a few hours," therefore, until his borrowed powers fade and vanish, Superman is equipped with Cosmic Boy's power of super-magnetism, Saturn's Girl's "power of telepathic thought-casting," and Invisible Kid's "power of invisibility" (S No. 172: pts. I-III—"The New Superman!"; "Clark Kent—Former Superman!"; "The Struggle of the Two Supermen!"). (TGSB)