During Superoy's career, young Clark Kent juggled the delicate balance between Smallville High School attendee and costumed crusader. Splitting his time between his 20th century tales and adventures alongside the Legion of Super-Heroes in the 30th century, he had several opportunities where he could've accidently jeapordized his dual identity. Thankfully, his childhood pal Pete Ross already knew of Clark's secret when witnessing his transformation during a camping trip. As such, Pete several times assisted his buddy by creating distractions that allowed Clark to become Superboy, and this led to Ross being invited to the Legion of Super-Heroes as an honorary member.
However, as an adult Ross and Kent drifted apart, whereby they only met each other on occasion. During one such incident, Superman revealed his double identity to Pete's son Jonathan. After aiding the Man of Steel several times, an alien race proceeded to kidnap Jonathan and take him to their world where he would be instrumental in saving millions of lives, according to the Legion. When Superman refused to retrieve his friend's son, Pete's mind snapped and utilizing technology developed by Lex Luthor, Ross became Superboy brought from the past to the present. Attempting to assassinate his former friend, ultimately it was Superboy in Ross' body who turned that tables on him. Eventually, Superman did rescue Jonathan and returned him to Earth-One to reunite with his father.
A similar father and son dynamic occured on Earth-Two, only it was Pete's counterpart Heinrich Mueller who was the son, inspired by his scientist father to become a supersoldier of the Nazis. Seeking revenge against Superman for thwarting so many German schemes during World War II, Mueller was injected with liquid Kryptonite which transformed him into the superstrong irradiated Atoman. Employed as Henry Miller at the Daily Star, the villain attempted to form fake friendships with the newspaper staff in order to get close to the Man of Tomorrow himself. In a final duel, Atoman seemingly plunged to his death when, in fact, he'd lay comatose for decades before reviving himself in the 1980's on Earth-One. After battling that World's Finest team, Superman brought Mueller back to his homeworld where Batman was waiting alongside Earth-Two's Superman and Robin. Thus ended the lengthy yet brief career of the Atoman.