Despite always seeming buddy-buddy, Iron Man and Captain America would absolutely hate each other in real life. Tony Stark is the symbol of American capitalism and excess as his small fortune has made him nearly invincible, despite being a womanizing drunk; Captain America, on the other hand, is a throwback to the Roosevelt-era politics of the '30s and ‘40s that championed social justice and the distribution of wealth to the lower classes.
In Marvel’s most successful crossover event in recent years, Civil War finally ripped the smiling veneer off of the Avengers’ head honchos and pitted them against each other in a bloody battle where sides were taken and lives were lost.
The story dealt with a new initiative that would make it mandatory for heroes to register their identities with the government and become U.S. employees. Stark championed this cause because he felt it would increase security and decrease the appearance of violent vigilantes, but the Cap gathered a group of rebel Avengers to oppose it, citing the inherent dangers with being revealed to the public and becoming tools of the government.
With the heroes turned against one another, Stark and Cap finally came to blows that resulted in the defeat of the anti-registration group and the eventual assassination of Captain America.