The cave
In Iron Man, Tony travels to Afghanistan to demo the Jericho missile. His convoy is attacked and he's wounded by shrapnel from his own weapons. He wakes up in a cave, a prisoner of the Ten Rings, with an electromagnet in his chest that keeps the fragments from reaching his heart. The device was made by Yinsen, another prisoner.
Forced to build a Jericho for his captors, Tony secretly builds a miniature arc reactor and a crude suit of armor, the Mark I. Yinsen dies in the escape. Tony comes home and announces the company will stop making weapons.
In Malibu, he perfects the armor and discovers that Obadiah Stane, his father's partner and his right-hand man, was selling weapons to both sides and ordered the kidnapping. Stane rips the reactor out of Tony's chest and puts on a giant suit of armor. With Pepper Potts's help, Tony wins. At the press conference the next day, he ditches the script and says: I am Iron Man.