Unlike Captain America Iron Man was one of the original Avengers. Iron Man was around much earlier than the formation of the Avengers. Iron Man was created by the master Stan Lee along with Larry Lieber, Don Heck and Jack Kirby Tales of Suspense #39 back in March 1963.
Stark was a billionaire playboy/genius who suffered a chest industry during which the people who captured him tried to force him to build a "weapon of mass destruction" for them. Iron Man instead created a suit made of iron nonetheless that fought helped him to fight off his captors. The suit was later modified using the technology from his own company Stark Industries in order to help fight crime. The central source of his power and the device within his chest also keeps him alive. Iron Man's super powers include his genius intellection, a cyberpathic link with his armored suit, superhuman strength, energy repulsors, missiles, and durability.
Stan Lee created Iron Man as a commentary on the Cold War. Iron Man represented the advancing technology in fighting. Lee used Iron Man to represent the advancing technology in the arms race with the Soviet Union during the Cold War. As time passed and the Cold War evolved Iron Man, Stark, and everything associated it used the changing times to help create an evolutionary path with the character. Like within the film some of the trends associated with the character were corporate crime and terrorism.
Throughout the years Iron Man has represented one of the most interesting comic book characters because of the symbolic nature of his character. Iron Man has also had a wide variety of allies/villains grace the pages of his comics. Iron Man's long standing allies are his assistant/sometimes love interest Pepper Potts. Tony also has his friend James Rhodes also known as Rhodey who became War Machine. Rhodes relationship started way back when the two met in Vietnam, and although they have had their ups and downs their friendship remains strong.
In 2008 comic book films took a different path. 2008 marked the release of two landmark films in the genre, The Dark Knight, and Iron Man. Iron Man took a turn towards the realistic, and used the concepts of corporate crime, and terrorism to help launch Tony Stark to the path as Iron Man. Tony Stark was played by the amazing Robert Downey Jr. Downey Jr. is the perfect embodiment of everything Tony Stark. While the first film is excellent the second film proved to show the quality dipped a little. I am excited to watch him grace the screen again in The Avengers this week, and I am hoping the third installment proves to turn things around.