Downey plays Tony Stark, the smooth, brilliant billionaire playboy, heir to his father's defense corporation. Stark Industries specializes in creating weapons of mass destruction, and as the film opens Stark is showing off his new toy in the Middle East. His vehicle is attacked and he is captured by terrorists. These villains are intent on forcing Stark to build them a bomb, and they hold him hostage in a cave. Stark must also create a device to place around his heart to keep shrapnel from entering his heart and killing him. In this cave, Stark builds the prototype of Iron Man, a giant metal suit of armor. Once he escapes in this original suit, Stark has a change of heart, and a few ideas on how to refine his armor to something more practical.
The creation of Iron Man in the hands of Downey is one of the joys of the film. As Stark, Downey is in his comfort zone of sarcasm as he flirts incessantly with his assistant, Pepper Potts (Gwyneth Paltrow) and tests out suits until he gets it right. This Iron Man film was maybe more vital to the character than any Superman, Spider Man, or Batman film because for many this was a formal introduction to the character. Favreau understands this and has the pacing down pat. The introduction of Iron Man strutting his stuff is in a glorious day time sequence where we can see everything.
Iron Man may be lacking a strong villain, but Jeff Bridges' jealous Obadiah Stane comes as close as possible. The final showdown between Stane and Stark is more thrilling than anything you can find in Iron Man 2, and it isn't even the best part of this original film. The Avengers film series started with the best, and it's not that any of the other films are bad, it's just that none of them ever had the charm of the original Iron Man.