Moments before the distant planet Krypton died, a small rocket was launched from its surface. This rocket made its way across space to crash land on Earth, where it was discovered by John and Mary Kent, a childless couple (both aproximately 50 years old). They rescued the rocket's sole occupant, an infant boy, just as the rocket was consumed by flames. They first took the child to an orphanage, but soon returned to adopt him.
The child, who the Kents named Clark, was unusually strong and healthy. In fact, by the time he was a young man, he was strong enough to bend thick steel bars in his bare hands. He could also outrun any automobile and leap over buildings. He became so tough that it was reckoned that only a bursting shell might damage his skin.
The Kents taught Clark about truth, justice, and the American way. He was a young man when they passed away, and their deaths greived him greatly. He resolved to use his special abilities to champion the morals the Kents had taught him, and moved to Metropolis to get a job at a major newspaper, where he would be able to find out about people in need of his help.
At first the Editor of the Daily Star wasn't interested in Clark. Undaunted, Clark changed into the colorful costome he'd contrived to distinguish his superheroic activities from his every day life, then proceded to prevent a lynching. Clark reported the story of his "Superman" alter-ego's actions, and won a job at the Daily Star.
Working at the Daily Star, Clark met girl-reporter Lois Lane. He was immediately attracted to her, but she wasn't at all interested in the meek, rather spineless facade Clark had created to distinguish himself from his heroic alter-ego. But Lois was strongly enfatuated with the ultra-manly Superman.
As time passed, Superman's powers continued to increase. Almost without him realizing it, his great leaping ability evolved into gravity-defying flight. Bursting shells, which might've hurt him at the start of his costumed career, eventually had all the effect of soap bubbles popping against him. He developed the ability to see through anything but lead, and to emit heating rays from his eyes. He could hear the faintest sounds. He could see better than the strongest telescope or microscope with his naked eyes. He became so fast that he could break the lightspeed barrier and even move through time.
Having become so powerful and invulnerable, Superman was more than a little surprised to find out that a chunk of rock could render him helpless... After his first encounter with kryptonite, he traced the origin of the material and learned (for the first time) about Krypton and his birth parents, Jor-L and Lara. He learned that his own Kryptonian name was Kal-L.
Eventually, a villian called "the Wizard" cast a spell that caused Clark Kent to forget that he was Superman. Thinking himself a normal human with no secret identity to hide, Clark began to behave according to his true, inherently heroic nature. As a crusading investigative reporter, Clark Kent became almost as big a scourge on the criminal element as Superman had been. Now seeing the real man for the first time (rather than the superhero or the milksop facade), Lois fell in love with Clark Kent, and the two were soon married. It wasn't long before Lois realized that her new husband was actually Superman. She managed to get the spell reversed and settled into life as the secret wife of Superman.
Clark eventually became editor of the Daily Star. Although he showed the physical appearance of aging, his powers did not diminish.
When Superman was almost seventy, he joined his young Earth-1 counterpart as well as a host of heroes from various Earths (and other worlds) in the Battle against the Anti-Monitor in the Crisis on Infinite Earths. He struck the final blow himself. With the reality of his world eliminated by the Universal reformation, Superman, Lois, the Earth-Prime Superboy, and Alexander Luthor of Earth-3 retired to a Paradise-like alternate dimension.