Captain America and Iron Man are two of the most prominent heroes throughout the Infinity Saga of the Marvel Cinematic Universe, each appearing first in a solo movie and making grand departures from the franchise in Avengers: Endgame. They're the closest thing the first three phases have to main protagonists, as they're always at the center of most of the world's major events.
The two are very different characters, with the films going out of their way to compare and contrast their personalities, beliefs, and abilities. However, they're not complete opposites, and throughout the films, they show that they have almost as many similarities as they do differences.
10 Similarity: They're Both Convinced That They're Right
Tony Stark and Steve Rogers are both very opinionated people with strong views. Whenever they argue, neither of them tends to actually listen to what the other is saying, instead simply holding true to their opinion and disregarding the other's.
This tendency rears its head in both The Avengers and Avengers: Age of Ultron, but it is in Captain America: Civil War that it's most prominent. With neither willing to budge from their stance on the Sokovia Accords, relations between the two crumble until it drives the entire team to fight one other.
9 Difference: Iron Man Is Arrogant, While Captain America Is Humble
Although ultimately a very heroic figure, Tony Stark is widely recognized for his personality flaws. His impulsive nature and enjoyment of annoying others aside, Tony has a large ego and isn't afraid to let others know it. Many throughout the series comment that Tony is beyond confident, bordering on arrogant.
Although he has plenty of his own flaws, Steve tends to be humble. While he doesn't put himself down and can indulge in showing off from time to time, Steve doesn't seek fame or fortune. It's one of the many reasons why the Super Soldier serum works so well on him, exaggerating his modest and well-meaning nature.
8 Similarity: They're Heroes Even Without Their Iconic Gear
Iron Man's suits and Captain America's shield are two of the most iconic items in the entire MCU, matched only by Mjolnir in how embedded they are in the public consciousness. They're also both of immense help to the two, with Steve's shield being the weapon he's best suited to, and the suits giving Tony a huge amount of power and versatility.
Despite this, the MCU has taken great pains to show that these pieces of equipment only help them, not make them heroes. In Captain America: The First Avenger and Avengers: Infinity War, Steve fights without his shield, and Tony goes without his suit to great effect in Iron Man 3.
7 Difference: They Naturally Fall In With Different People
Although ultimately friends with one another and both capable of socializing with the other Avengers, Steve and Tony don't have too many close friends in common. The Avengers as a whole vary between good friends and colleagues who can work together, but there are several intense friendships within the group, often centered around Steve and Tony.
Steve is close with Sam Wilson, trades battle banter frequently with Thor, and bonds with Natasha Romanoff over their shared struggles overcoming their past. Conversely, Tony's closest friend is Rhodey Rhodes, and he also goes to Bruce Banner for help with any number of things, and acts as a mentor figure to Peter Parker.
6 Similarity: They're Both Quick-Witted Conversationalists
Tony Stark's most notable character traits are his wit and his snark. There is almost no situation in which he can't find a quip or a joke to make, and even characters he irritates have to admit he's funny. Tony trades quips with Loki, Ultron, his teammates in the Avengers, and almost anyone else he speaks to.
Despite being more polite and friendlier in conversation, Steve also shows himself to be fully able to snark and joke. Although he does it much less often, he's shown himself able to be witty and snarky with Natasha Romanoff, Nick Fury, Tony himself, and a number of the MCU's other most cunning conversationalists.
5 Difference: One Prefers To Fight Up Close, The Other Prefers Ranged Combat
Although both immensely capable in combat, Captain America and Iron Man fulfill different roles on the team. Tony's suits give him a huge amount of strength and stamina, making him fully capable of holding his own in melee combat, and Steve can use guns and throw his shield to fight at range. However, that's not what they're good at.
Instead, Tony tends to use his repulsors and missiles to fight from a distance, often acting as a skirmisher or aerial support. Steve works best in the middle of the fight, using his strength and his shield up close to deal damage to their foes and to draw attention away from the others.
4 Similarity: They Can't Help But Respect Each Other
The characters' differences often see them clash, going beyond mere jabs to open mockery and even physical violence in Age of Ultron and Civil War. They disagree in almost every film they both appear in, and much of the tension in the first half of The Avengers is driven by their inability to work together.
However, every film they're in also sees them show a large amount of respect for each other... eventually. The two are friends, despite their differences, and they each admire the other's good points and trust each other. The moments they admit this, such as during Civil War and Endgame, are rare, but they're present.
3 Differences: Steve Is Stoic, & Tony Is Volatile
While neither Steve Rogers nor Tony Stark is a patient mastermind, they show differences in how they react to situations. They each have buttons that can be pushed to make them act recklessly, but on the whole, Steve is better at taking stock of a situation and processing events, whereas Tony is more impulsive and driven to act on his emotions.
These are the traits that feed Zemo's plan in Captain America: Civil War. He trusts Tony to act on his emotions when the Avengers are threatened and again when he learns the truth of his parents' deaths. In both that film and several others, Steve is shown to be less ruled by his emotions, sometimes for the better.
2 Similarity: Both Are Willing To Sacrifice Themselves
In The Avengers, Steve sees Tony as a selfish glory-hound, one who enjoys pretending to be a superhero but isn't willing to genuinely sacrifice himself for the greater good. Steve, conversely, shows a willingness from the start, upending his entire life to thwart Red Skull's plans in The First Avengers.
Although he's often insightful, this is one time Steve is wrong. He's proven wrong in The Avengers itself, when Tony almost dies flying the nuke into space, and more poignantly in Endgame when Tony dies after using the Infinity Stones on Thanos. Ultimately, they're both equally heroic when it comes to their willingness to die for others.
1 Difference: Their Changing Attitudes Towards The Government
As Captain America, Steve Rogers is a special operative and a propaganda tool for the US government. Conversely, Tony resists attempts by the government to control him, most notably taunting the government for their inability to take away his suits in Iron Man 2. Events see them begin to change positions, however.
SHIELD's Tesseract experiments, alongside Project Insight and ultimately the existence of HYDRA within SHIELD all see Steve become much more opposed to authority, doing what is right no matter what. After several high-profile mistakes, Tony becomes much more open to the idea of oversight. In the end, they swap views but remain staunchly opposed to each other regardless.