The Reason: It was during the war, when comics were first used to relieve people's tensions. In the Second World War, America needed new heroes to personify the country and uphold justice. A number of super heroes had already been introduced.

The Birth: It was in June,1938 when Jerry Siegel and Joe Schuster's creation hit the American market. This new superhero which first established itself in Action Comics #1 made an instant impact on the general public.Thus Superman was born.

The Alter-Ego: Superman was adopted by chance, by the Kents, and was christened as Clark Kent. Clark was taught human values,goodness and justice by his parents who always emphasized truth, justice and liberty the American way. He grew to become a mild mannered, gentle person who never really used his powers for his own benefit. Clark later became a reporter with the Daily Planet. Apparently, he got his job by turning in an exclusive on Superman when the Kryptonian first hit Metropolis. In doing so, he also caused a long term rivalry with his collegue; Lois Lane (See Lois Lane) who felt that she had been scooped by a total stranger with no field experience whatsoever. Clark soon gained reputation for one of the finest reporters in the business, leading him to win many awards. Later, his reputation won him a job with Newstime as the editor of the magazine. Unfortunately, his mind at the time was being messed around by the Eradicator (See The Eradicator) and it eventually got him fired from his new job within no time. But Clark was once again accepted back at the Daily Planet and has been there ever since.
As for Lois Lane, he later got into a relationship with her. As it got a bit rocky, he started going out with Catherine Grant, something which didn't last very long. But as time went by he eventually got engaged to Lois. They did have their share of troubles and there was a breif gap which left Clark gasping as Lois called off the engagement. But in the end, the couple finally got married.

The Legend: The planet Krypton had become unstable and it's natural destruction was invetible. A leading scientist, Jor-El and his wife decided to give their baby a chance at life rather than suffering the fate of the rest of the populace, by rocketing him to earth, where they thought he would survive and grow to rulw over the inferior earthlings.
Kal-el's rocket crashed in a small farm in Kansas, where Johnathan Kent found him.

Superman's strengths include super-strength,super-speed,X-ray vision,heat vision,telescopic vision and super-hearing. And since Earth's gravity is much lighter than that of Krypton's, Superman is able to leap up to great heights, virtually giving him the power of flight.
As Clark Kent grew up, he evntually moved to Metropolis to become a journalist and a reporter with the Daily Globe. Later on he married his collegue and long time friend;Lois Lane. Superman was once killed by Doomsday; (See Doomsday)a beast bred to fight and destroy. By some miraculous chance, and with the help from his father and the Eradicator, he came back to life.
When Superman, soon after coming back to the world of the living, went to Coast City to fight the Cyborg, he was almost again killed, had it not been for the Eradicator who jumped in front of Supes to shield him from the Krytonite blast. However, the element filtered through the Eradicator and hit the Man of Steel, rejuvinating him instantly. But the long term effect of this proved to be quite lethal. Apparently, Supes metabolism had been altered and he was incapable of expending the cast amount of energy that was accumulating in his body. Evetually, that problem was taken care of with some help from the Parasite; a being who could absorb the energy of any living being. (See Parasite)
Over the years Supes has faced many super villains, some of whom were even more powerful than the Man of Steel himself. But as always, he has always survived through thick and thin and still continues the never-ending fight for justice.
Sometime after his apparent death, another Superman body was found which according to the tests proved to be 100% kryptonian, which led Superman to become unsure of himself that he might be a clone. However it turned out to be just one of Brainiac's mind games. And months later, while in battle with the Parasite he was dragged off by the Tribunal and judged guilty for the death and destruction of Krypton. Though the Tribunal was tough for him, he managed to escape and set things right.

And after his marriage to Lois Lane, he lost his powers entirely, then regained some new energy based powers, then split into two whom people began calling Superman Red and Superman Blue, and finally returned to his normal self with normal powers.