Before the theatrical release of Iron Man in 2008, Tony Stark was a bit of an also-ran when it came to Avengers. Sure, he was a founding member of the famous superteam, but his individual comics never sold particularly well. Frankly, he was pretty far down the list of popular Marvel characters. He was more Dazzler than Wolverine, if you catch the meaning. Great Iron Man storylines were few and far between, and almost no one would call him a fan favorite. Then, Robert Downey Jr. happened, and everything changed.
While Iron Man is now firmly entrenched as one of the faces of Marvel, that hasn’t necessarily changed anything in the world of comic books. Tony Stark is certainly featured more prominently in Marvel’s publishing (and marketing material), but that still doesn’t mean anyone actually likes him. Most comic fans still like to root against Tony, and with good reason. He’s easily one of the least likeable Avengers when it comes down to it, and his comic book iteration remains consistently egotistical and obnoxious. It’s time for fans to stop letting Iron Man coast on Robert Downey Jr’s affability and face what he really is: the most overrated Avenger of all time.
Iron Man was once the Avenger who protected his secret identity with the most intensity. He feigned employment as a "bodyguard" to Tony Stark even to his closest teammates. Eventually, Stark got bored (as he is wont to do) and revealed himself to the world. It wasn’t long before he decided that everyone else should reveal their secret identities, too.
This led to the superhero Civil War, which included Iron Man convincing Spider-Man to publicly unmask. This, of course, led to Aunt May getting shot. Tony Stark, meanwhile, built robot suits for all of his loved ones so he wouldn’t have to face the same consequences. Way to go, Tony. You're a class act.
Robert Downey Jr’s portrayal of Tony Stark is popular because of he is able to toe the line between lovable and frustrating. Sure he's arrogant, but he manages to make it endearing. While RDJ manages that fine distinction with precision, the comic book version of Iron Man falls firmly on the "annoying douchebag" side.
Tony Stark always thinks he knows best, not just for himself, but for pretty much everyone on the planet. He often tries to enforce his will on others and refuses to listen to anyone’s feedback, mostly because he sees himself as smarter than everyone else. He has an entire team of dedicated and compassionate superheroes to help him out, yet Tony insists on doing everything himself. He's basically Dr. Doom with a slightly better skincare regimen.
Although he helped found the team, Tony Stark has been mistreating his fellow Avengers pretty much since the beginning. Iron Man is bossy and controlling to the extreme, often frustrating his teammates with his constant need to be in charge of everything. It's doubly annoying since he almost never knows how to lead effectively once he takes power.
But honestly, that's kind of the best-case scenario. When he isn't trying to lead, Stark is outright mistreating his teammates by insulting their intelligence and meddling in their personal lives. Sure, Tony Stark lest the Avengers live in his mansion, but he also felt comfortable monitoring their every move. Not exactly “trusted leader” material.
Captain America is the clearly-defined moral center of the Avengers, but that hasn’t stopped Iron Man from trying to usurp the role. The problem is, unlike Cap, Tony Stark isn’t exactly iron-clad when it comes to his personal beliefs.
At first, Iron Man fervently protected his secret identity, but then he sought to "out" other heroes in the first Marvel Civil War. Then he started the second Civil War by fighting against Captain Marvel’s use of predictive justice, despite regularly practicing the same thing with his Illuminati friends in the recent past. Basically, his moral philosophy seems to be "whatever is the most convenient to me at the time."