Superman was originally Kal-El, the last survivor of the planet Krypton, raised by Jonathan and Martha Kent as their son Clark Kent. He soon discovered that he had superhuman powers, and as a boy and a teenager, he used them to fight evil as Superboy. In his first adventure as Superboy, he teamed up with the Flying Fox (a young Bruce Wayne) to defeat the Ultra-Humanite, while Jonathan Kent tried to warn Thomas and Martha Wayne about their future murder, having discovered it through a chronoscope. (The circumstances of that first team-up were kept secret from Bruce Wayne for decades. Later, Superboy teamed up with Bruce Wayne again, in his identity as Robin.
He officially began his career as Superman in 1938, after moving to Metropolis and going to work for the Daily Planet. Superman eventually married Lois Lane, and they had two children- Joel (who never developed powers due to Lex Luthor exposing him to gold kryptonite while Lois was pregnant with him; he was believed to have died in Vietnam) and Kara (who eventually became Supergirl). Kent also rose to become editor of the Daily Planet.
However, in 1979, Superman's life was destroyed after decades of planning by Luthor. Joel Kent, who had survived Vietnam, was turned against his family, and killed Kara with temporary Luthor-granted super-powers before those same powers caused his death. Lois, who had struggled against cancer for years, was killed by Luthor shortly afterwards. In the process, Kent's identity as Superman was revealed to the world. Superman became determined to hunt Luthor down, and spent a decade searching- and while he was gone, Luthor's agents ensured the death of Superman's friends. Superman finally caught Luthor in 1989, but had his powers stolen by gold kryptonite. However, in an attempt to stop Luthor- revealed as the Ultra-Humanite- from stealing his body, he accidentally killed him. Submitting himself to the authorities, he was sentenced to ten years in the Phantom Zone.
After being released, he restored his powers using chemicals left behind by the Ultra-Humanite, as well as giving powers using those same chemicals to Joel Kent's son Knightwing. Superman continued to adventure for the next thousand years.