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. 