Tony Stark (Robert Downey, Jr.) is the head of Stark Industries, a major military contracting company he inherited from his deceased father. Stark is an inventive genius and wunderkind; however, he is also a playboy. After being interviewed by Christine Everhart, he charms her into sex that night. The next morning Stark's disapproving assistant, Virginia "Pepper" Potts, sends her off.
While his father's old partner, Obadiah Stane (Jeff Bridges), takes care of day-to-day operations, Stark flies to war-torn Afghanistan with his friend and military liaison, Lieutenant Colonel James Rhodes (Terrence Howard), for a demonstration of Stark's new weapon, the "Jericho" missile. Afterward, Stark's military convoy is attacked and he is critically wounded. Stark finds himself the prisoner of an Afghan terrorist group known as the Ten Rings. An electromagnet has been embedded in his chest by fellow captive Dr. Yinsen to keep shrapnel from working its way to his heart and killing him. The Ten Rings leader, Raza, offers Stark his freedom in exchange for building a Jericho missile for the group. Yinsen later confirms Stark's suspicion that Raza will not keep his word.
During his three months of captivity, Stark and Yinsen secretly build a crude suit of armor powered by a miniature arc reactor, which Stark builds to power his electromagnet. The terrorists finally grow impatient and give Stark 24 hours to finish. The deadline expires before the suit is fully activated, so Yinsen distracts the guards while Stark powers up the suit. The now-armored Stark battles his way out of the caves and finds the dying Yinsen, who tells him not to waste his life. Stark burns all the terrorists' munitions and flies away, only to crash in the desert; Stark survives, but the prototype suit is destroyed. After being rescued by Rhodes, Stark announces that his company will no longer manufacture weapons. Stane advises Stark that this may ruin Stark Industries and his father's legacy.
Stark begins focusing his energies on building an improved version of his suit as well as a more powerful arc reactor for his chest. Later, during Stark's first public appearance after his return, reporter Everheart informs him that Stark Industries weapons, including the "Jericho", were recently delivered to the Ten Rings and are being used to attack Yinsen's home village. He also learns that Stane is trying to oust him from his own company. Enraged, Stark dons his new armor and flies to Afghanistan. The Ten Rings fighters prove no match for Stark, and they are quickly dispatched. While flying home, Stark is shot at by two F-22 Raptor fighter jets. He tells Rhodes his secret identity in an attempt to get the attack called off, but manages to escape on his own.
Stark sends Potts to hack into the company computer system. She discovers Stane has been supplying terrorists with Stark weaponry and hired the Ten Rings to kill Stark, but the group reneged on the deal upon discovering who the target was. Potts later meets with Agent Coulson of the "Strategic Homeland Intervention, Enforcement and Logistics Division", a counter-terrorism agency, to inform him of Stane's activities.
Stane visits the Ten Rings and, after obtaining the pieces of the destroyed prototype suit, has the group eliminated. He then reverse engineers his own suit from Stark's first; however, his scientists cannot duplicate Stark's arc reactor. Undeterred, Stane ambushes Stark in his house, uses a sonic device to paralyze him, removes the arc reactor from Stark's chest and leaves him to die. However, Stark manages to get to and reinstall his original reactor. Meanwhile, Potts and several S.H.I.E.L.D. agents go to arrest Stane, only to be attacked by him in his now functional suit.
Stark races to the rescue but is outmatched by Stane, as his old reactor is underpowered for his current suit. He lures Stane atop the Stark Industries building and instructs Potts to overload the full-sized arc reactor in the building. This unleashes a massive electrical surge that knocks Stane unconscious and sends him falling through the ceiling directly into the reactor, apparently killing him. Pepper fears that she's killed Stark, but a scene showed rolling on his back to avoid the electrical surge.
By the following day, the press has dubbed the mystery person, Stark in his armor, as "Iron Man". Since it was Stark fighting with Stane, Agent Coulson hands him an alibi that puts him on his yacht at the time of the attack with Pepper cleaning up his cuts and bruises with makeup. Before speaking at a press conference, Stark briefly makes an attempt to establish a romantic relationship with Potts, but she refuses. Stark starts to tell the cover story given to him by S.H.I.E.L.D., but then announces that he is Iron Man.
In a post-credits scene, S.H.I.E.L.D. Director Nick Fury visits Stark at home, and, noting that Iron Man is not "the only superhero in the world", says he wants to discuss the "Avenger Initiative".
Source : Wikipedia
