Superman's mythology is a living document, an ever-changing tapestry in which Justice League is just the most recent thread. It does, however, give a generation of comic book fans a perspective on "their" Superman which has not really been explored before on the big screen.
Grant Morrison, generally accepted as one of the great Superman writers of the last 20 years, was asked at the time about changes to Superman's mythology in Man of Steel and to Iron Man's significant changes in the franchise's third film. His response was worth considering:
"In Australia, Aboriginal artists, every generation goes in and repaints the cave paintings. And they all tell the same stories over generations. And that's what we do. The human species tells the same stories over and over again. Stories of heroes and villains. And I think we have to update them for each new generation," said Morrison. "Any fans who cling on to maybe a version of something they read when they were children are really just hanging on to a past. The world's moved on. There's new children. They want their version of it. So I think it's very important to freshen these things up and to update them and to move them forward and to look at them in the context of all the things we're interested in now."
For a generation born in the '80s, our "version" of Superman, the one that most of us connect with and the character we think of when someone says "Superman," had been gone since around 1999 or so, his history and attitude quietly changed until he was nearly-unrecognizable in some respects, in order to appeal to a different demographic. The version that replaced him vanished in 2011 when they rebooted the whole publishing line. Our version, in turn, sprang to life in 1986 after the previous one was deemed too quaint for his own good -- and while the pre-Crisis on Infinite Earths Superman informed the 2000-2011 more significantly than the 1986-1999 version, those influences did not completely disappear when a recognizably '90s-inspired Superman returned to the comics in 2015's Superman: Lois and Clark.
The process is cyclical, and it has been for years. Before we had giant, continuity-altering, time-travel stories to "force" the change, we had the simple act of a writer consciously changing the depiction of a character to better reflect the times. Superman, when introduced, wasn't "The Man of Steel," "The Man of Tomorrow" or "The Last Son of Krypton" but the "Champion of the Oppressed." He fought fat-cat bankers who gamed the system and screwed the little guy but years later he was busting commies just like any other American pop-culture hero. In the '70s, his book became increasingly science fiction-oriented, which continued until the '80s when they officially hit the "reset" button the first time.
There is, as longtime Superman: The Man of Steel artist Jon Bogdanove recently recounted to us, a disagreement even among the professionals who make Superman comics about just how he should be handled. Is he an alien who feels out of place? Is he a god merely masquerading as a man? Is he a farm boy ill-at-ease with the expectations placed on his shoulders? Is he the all-American kid? A little of everything?
For creators like Bogdanove, and current Action Comics writer Dan Jurgens, Superman is Clark first. This is one of the things that the film universe largely seems to understand (even if it not always executed perfectly): the appeal of exploring who Superman is and why he does what he does.
In the past, films have seen him as a generally good guy and was raised right, with not much needed beyond that. Still, exploring Clark before he was Superman has some value, for a reason made explicit in both the Superman comics of the post-Crisis era and the Justice League movie:
In Justice League, when pressed by Alfred as to why it was so important to resurrect Superman, Batman gives a variety of answers that fail to pass muster with his father figure. One of them, finally, connects. The answer?
"He's more human than I am," Batman says. "He lived in this world, fell in love, had a job, despite all that power."
"The world needs Superman," Bruce adds. "The team needs Clark."
That fundamental part of most modern interpretations of Superman had never really made it to the big screen before Snyder: the idea that Batman is the real guy, and Bruce Wayne is the mask he wears in the daytime. Superman, meanwhile, is a costume that Clark Kent puts on.
Batman is driven by guilt and rage and his truest, most recognizable self is the one who dresses up in body armor and pummels people who remind him of the guy who killed his parents. He wears the costume to strike fear into the heart of criminals who are, by nature, "a superstitious and cowardly lot."
Superman, on the other hand, just does what he does because it's the right thing to do, and he can.
Superman wears a costume to protect Clark Kent's loved ones, and to give himself a chance at a normal life in the off-hours. Clark is who he is, and Clark is a hero in his own right. He's an award-winning investigative journalist and when he's occasionally found himself without powers, that hasn't stopped him putting himself in harm's way for a story. Dressing as Superman, and NOT wearing a mask, is a calculated move. If he were wearing a mask, there would always be a question of who's under it, and so he would always be worried about protecting his identity. Not wearing one, and going out in public, gives people the impression that this is his life. The hope is that they assume when he's not Superman, he's off on another planet or in his Arctic Fortress or something. They don't think he's even got another life because, why would he?
(Seen in that light, incidentally, the idea that changing your hairstyle, posture and wearing glasses might ACTUALLY be a legitimate disguise for Clark, since nobody's looking for Superman to be anywhere else. I mean, we have no reason to assume that Donald Trump has a second life, either, so if you saw someone who looked a lot like him, would you accuse him of being President? Would people try to lobby him? Assassinate him? Probably not.)
And that's been the thing about the film adaptations up until now: "You will believe a man can fly" was the most important thing. Superman was always the most important thing. Clark was secondary--at best--and frankly it left the character a bit shallow and aloof. In the more modern setting of Snyder's films, it's about his struggles -- because without Clark Kent, Superman is basically just a costume.
Justice League is in theaters now.