Superman debuted in Action Comics #1 in 1938. He was initially completely invulnerable as well as inhumanly strong and able to fly. Like his classic predecessor Achilles, Superman has an obscure weakness and encapsulates the values of his society: truth, justice, and "the American way."
Batman debuted in Detective Comics #27 in 1939. He is dark and brooding, and he overcomes his problems and adversaries by applying a keen mind and a warrior's physique. Like Odysseus, Batman metes out justice while in disguise, and he is not above exploiting his enemies' weaknesses or slipping away while they are distracted.
Captain America was born for war; he was born mortal but became something more than human to overcome a seemingly unstoppable enemy. Like Beowulf, Captain America uses his sheer brawn and fierce devotion to a warrior ethic to defeat the unspeakable horror confronting his people.
The 1930s and 1940s are considered the Golden Age of comic books, when some of the most iconic and recognizable heroes were created. By the 1960s, the so-called Silver Age of comics dawned, bringing more complex and human heroes.
Spider-Man first debuted in 1962. The hero is more human because is a high-school kid who must deal with mundane problems almost as often as heroic ones.
Inspired by "Dr. Jekyl and Mr. Hyde" and "Frankenstein's Monster," the Hulk debuted in 1962. Epitomizing the growing frustration of society and the desire to lash out as well as control those feelings, Dr. Banner and his alter ego encapsulate a society in turmoil.
Debuting in 1963, the X-Men are a team of super-human teenagers. In a nod to the baby boomer generation's growing power, as well as their "alien-ness," the X-Men tackle increasingly strange and powerful enemies, many of which are a legacy of the previous generations' sins (e.g., Magneto).