Superman. alias reporter Clark Kent, was the last survivor of the planet Krypton. He was found by an unknown individual after landing on Earth and taken to an orphanage, where he grew up and decided to use his powers to fight evil. He mainly dealt with ordinary criminals such as gangsters, hijackers and foreign spies, although he occasionally fought with such fantastic adversaries as the Mad Scientist, the Bulleteers, and the Mechanical Monsters.
It's unclear whether or not he knows he's from another planet, or if Kal-El is his birthname. Superman #19 poses the possibility that the events of the Fleischer cartoons actually exist on Earth-2 as fictionalized accounts of Superman's adventures, which might explain some of the differences.