Stark inherited a large American company called "Stark Industries" when his father died. He was badly injured by a bomb in an attack planned by people who did not like him running his company. Shrapnel from the explosion was moving towards his heart. This would have killed him, but a scientist called Yinsen who was with him made a magnet for his chest which would keep the shrapnel away. In the movies, he makes an "arc reactor" which is put into his chest to stop the shrapnel.
Yinsen and Stark secretly build a heavy suit of armor which they plan to use to escape. However, during the escape, Yinsen dies so that the kidnappers will be distracted from Stark escaping. Stark escapes safely and goes back to America. He makes a better suit and uses it to fight evil.