Superheroes originated in comic books in the United States back in the 1930's, the most famous, if not the most popular, being Jerry Siegel's and Joe Shuster's Man Of Steel - Superman. This lead to many other superheroes being created and the first superhero "motion picture" around 1940, during the time of the Second World War. In these films, superheroes would help war efforts and bring the action closer to home, fighting gangsters or stopping evil criminals with plans to destroy the world.
In 1966 Adam West starred as Batman in the television show of the same name, and the two most significant films following that are undoubtedly Richard Donner's 1978 film Superman starring Christopher Reeve and Tim Burton's 1989 film Batman 1989 starring Michael Keaton. These films, as well as having many gender stereotypes, also portrayed superheroes as people who would be there to save the day whenever and wherever they were needed.
But when American Airline Flight 11 and United Airlines Flight 175 crashed into the World Trade Centre, or the Twin Towers, in 2001, the superhero genre would change forever. This event meant that these indestructible characters had new roles to fulfill, ones which wouldn't have been thought acceptable in the past. If the Germans had defeated Captain America (or whoever the Superhero might be) in films throughout World War Two, then kids might have lost hope in America ever winning the war. After all, if these superheroes couldn't beat them - who could?
It was a similar story over in Britain. Had the German spies escaped the feathered clutches of Big Eggo, or had Hitler successfully bombed and captured Lord Snooty, would the nation's youth have given up hope?
In the years post 9/11 superheroes could no longer be undefeatable good guys who won every battle straight away, and were always at the right place at the right time, with the ability to save everyone. Sometimes the bad guy would have to escape and innocent citizens would have to die, proving that superheroes weren't always to be relied upon, and sometimes they even revealed a slightly darker side to themselves.
Of course, the main fear surrounding 9/11 is terrorism, and superhero films constantly seem to display a "war on terror" theme. Two of the three Iron Man films have pinpointed on terrorists as the bad guys, as did several of Batman's enemies. An important quote from Bane to Batman is:
"So, as I terrorise Gotham, I will feed its people hope to poison their souls. I will let them believe they can survive so that you can watch them clamoring over each other to 'stay in the sun'. You can watch me torture an entire city and when you have truly understood the depth of your failure, we will fulfill Ra's al Ghul's destiny... we will destroy Gotham."
I'll finish with the first Spider Man. Filmed at the time of the attacks on 9/11 several scenes showed the World Trade Centre, but had to be edited out (for obvious reasons). After shooting had finished, Sam Raimi added an extra scene portraying a group of people throwing objects at the Green Goblin and yelling "You mess with one of us, you mess with all of us", as a tribute to the people of New York city.
In conclusion, superheroes have been affected dramatically by the shocking events of September 11th. They can no longer be relied upon to be at the right place at the right time, and save everybody before jailing the bad guy. Like it or not, they will never be the same again, in films or in comics.