His adopted parents revealed the rocket and his foreign heritage to their son when he was 18, leading Clark to the decision that he would become a hero in secret and use his powers to protect innocents.
He operated this way for seven years until he was forced to save a space-plane in front of crowds of people, then meeting reporter Lois Lane for the first time at age 25.
He is visited in this time by Cosmic Boy, Lightning Lad and Saturn Girl of the Legion of Super-Heroes from the 30th Century, an organization of super-powered teens inspired by his legacy.
They take him into the future and show him a world where he isn't different from everyone else.
His debut as Superman happens when he catches Lois Lane falling off of a Lex Corp building in front of crowds of people.