Superman. Batman. Captain America. Spider-Man. What comes to mind when you hear those names? Chances are it's their costumes, with all of the accessories and accouterments that come with them. Whether it's Iron Man's red-and-gold Mark III suit, the Punisher's iconic death's head, or even Rorschach's constantly-shifting visage, a superhero's costume is part of what completes the image and makes them stand out to the reader. Without a costume there's something missing. Why is that? Well, the answer might surprise you...
In The Beginning
It's important to remember that culturally speaking the superhero is less than a century old. We can trace the origin pretty firmly back to the debut of Superman, who first started smashing cars with his bare hands in 1938 with the debut of Action Comics #1. The original cover boasts the original superhero in his classic red and blue uniform, with his red cape flaring out behind him as he sends the bad guys running. It's an image that most people have seen at least once in their lives, even if they're not comic book fans.
There were heroes and crime-fighters before Superman though. Characters like Zorro, the Shadow, and the Green Hornet stood shoulder-to-shoulder with other pulp heroes like Doc Savage and Dick Tracy. Many of these characters had unique powers and special training, as well as costumes of their own. Those costumes tended to be more for function and form, and generally speaking they resembled the fashion of the day. The Green Hornet's topcoat, gloves, hat, and domino mask might be an emerald green, but they weren't too terribly different from what the average man on the street would wear on his way to the office. Same goes for the Shadow's hat and cloak, or Dick Tracy's eye-searing mustard trench coat. No heroes wore tights until Clark Kent came on the scene.
What changed was the inspiration for the character design. Previous heroes were inspired by fencing masters, cowboys, gunslingers, and detectives. Superman was inspired by carnies; specifically by circus strongmen.
It all makes sense if you look at Superman's costume. He has big, clunky boots, a seemingly pointless cape, a big symbol across his broad chest, and most tellingly he's wearing his underwear on the outside. That last fashion decision, which has led to endless questions from fans and fashion designers alike, is actually one of the most telling choices. According to comic book writer Grant Morrison, circus strongmen would often wear nude or colorful tights and over them wear some kind of codpiece with a big, impressive belt. The idea was to invoke powerful heroes of myth with a Herculean look and stature that would wow the audience. This little historical footnote makes it interesting (if not outright ironic) that superheroes are often compared directly to the heroes and gods of mythology, considering the amount of power many of them wield.
Where It Went From There
The massive success of Superman as a character quickly led to other characters made in similar molds. Batman, and later Robin are just two examples. So are the Fantastic Four, most of the Avengers, Spider-Man, and a dozen others besides. Not all heroes followed this mold, and in fact there are a number of characters from the pre-Superman era who still exist today. Even today those characters are not considered superheroes. Why? They simply don't look the part.