Everyone knows that Superman is a refugee from the doomed planet Krypton, raised by earthlings Ma and Pa Kent, who taught him to use his super powers for the benefit of earth. I almost said "truth, justice, and the American way," but we know that was added later. Yeah, Superman is the hero he always was, since that first comic was released in 1938.
But by the time Action Comics introduced Superman, Jerry Siegel had been working on the character for years. In early versions, he was an unwilling victim of a mad scientist who gave him strange and varied powers. The earliest version had him using those powers in a malicious way. The character went through several iterations, once as a time traveler, as Siegel collaborated with artists he knew before Superman had a name and a backstory. You can learn about those unpublished early versions of the Man of Steel in a 45-minute podcast at The Comics Code, or read a succinct account of the highlights at Boing Boing.