The man who changed Batman (and the first of the three names I'm going to point to) was Dennis O'Neil, and he shifted Batman back into the shadows from 1968.He was asked to reinvent the character, and he pretty much did just that. He picked up on elements of the mythos that had always been consistently implicit -but often pushed to the side due to sales, politics and censorship- and dragged them centre stage. He showed the editors at DC an essay by Alfred Bester on writing obsessed protagonists, and was given the go ahead to make that the new direction. It's always been talked about as simply going back to Batman's roots, but there is no hiding, reading the era back with the benefit of hindsight, what a radical move it was. This was the true shift in Batman comics, everything that followed has been an extension of that. The 70's gave us great stories like "The Joker's Five Way Revenge" and Steve Englehart's "The Laughing Fish," and it's these that really the stories that give us the modern Mr J, and both were hugely influential on the direction that David Goyer and Chris Nolan took in the first two films. To find Heath Ledger's joker we look not at Frank Miller but at the very first ever Joker story, then at these two 70's tales, and throw in Ledger's own anarchist take. And to read those stories is to pretty much read the Batman of the last 40 years. Other elements we take for granted that are directly attributable to O'Neil are the storyline of Bruce falling into a cave beneath Wayne Manor as child and being scared by bats, the creation of Ras Al Ghul and Bruce living in the penthouse of the Wayne building in Gotham. O'Neil didn't invent the term, "the Dark Knight," which first appeared in 1940, but he was the writer who popularised it in the 1970's as part of his 'new take.' The 70's is one of my favourite era's of Batman, for all the fresh ideas and a sense of youth and modernity in the art. All of these elements were key to Christopher Nolan's cinematic relaunch. (This is also the era that Grant Morrison clearly favours with his work of the last decade.)
It's also worth noting that O'Neil was named editor of the Batman books around the time of the mid-80's relaunch. He was the editor on both TDKR and YEAR ONE. He was the driving force, and would remain that way for over a decade until he ran out of juice and looked for retirement.
This era also saw the last gasps of the Comics Code Authority, and their regulations that O'Neil himself had helped to change in the previous decade. This is the CCA I mentioned earlier on, which was the beginning of artistic expression being controlled in comics. And this is where the second name comes into play; Doctor Fredric Wertham. Wertham was a psychologist who launched an astonishing attack on the comic book industry. Superman, he said, was propaganda to make American boys feel inferior. Batman and Robin, it seemed, was a way for subversive creative types to make all American boys into homosexuals. There were crime comics that, bizarrely, depicted crime. There were horror comics that, gasp, depicted horrors. This was in the same era as McCarthysim, when bizarre rhetoric was used to destroy the lives of writers and creators because establishment types always think these people have way to much power. The CCA was actually a self-imposed measure by the comic book industry, creating guidelines and rules of content, but it set up a huge schism; the more adult, interesting and radical art was pushed further into the fringes and away from the huge distribution network available to those who played the game. It also aided in the companies ripping off writers and artists, because the people most likely to be vocal about it were marginalised. (Sadly a practice that continues.) In the sixties and seventies, and much of the eighties, the comics were censored by the CCA. They were written within a straight jacket of talking down to the audience. The CCA had many rules that hampered storytelling, such as criminals not being allowed to be seen profiting from crime and also the methods of crime not being allowed to be seen. And if you're writing a Batman story, where you can't really show a crime being committed or profited from, you're going to struggle. Not least in reminding people of the trauma that created Batman. Sadly the impact of the CCA means we need to name Wertham as one of the key figures on the development of the superhero comic, but it's in essentially the same way that we credit Margaret Thatcher with the development of coal mining.
There is an era of Batman that some people recall, in which he would turn up to foil a vague plot by criminals -without us knowing what the plots were or why the criminals were even considered criminals- and then there would be a chase scene across giant furniture and ridiculous museum props, before the criminals would be caught and arrested. And they could be arrested by Batman, because he was a deputised law official to get around showing kids the actions of a vigilante. This wasn't the character that was created in 1939, and it's not the character we've had since the 70's. The strips are fun and enjoyable, and I like them as I like all eras of Batman, but they were written that way because of censorship, rather than out of any artistic desire. The schism I referred to can be clearly seen in superhero books of these decades, where some were the home of writers and characters who had no interest in rocking the boat or deviating from the acceptable route, and others who, as in every medium, wanted to push on to the next thing.
Some superhero comics moved with the times and others maintained a state of paralysis, forever holding onto what they were when the then current generation of writers had been children, and therefore had only had access to CCA approved newsstand fare. We don't need a history lesson of the 70's here, as scandal, corruption and financial problems turned old-fashioned square-jawed authority figures into villains and turned marginalised figures into anti-heroes. But it is worth noting that two of the most violent and disturbed 'heroes' in modern comics -The Punisher and Wolverine- both debuted in 1974, and Blade appeared the year before. Iron Man's battle with alcoholism in DEMON IN A BOTTLE was 1979 and back in'71 Green Lantern and Green Arrow had discovered that their sidekick, Speedy, was a heroin addict. Gwen Stacey died in a defining 1973 Spidey story. This is worth mentioning for two reasons; firstly is send a ripple across the whole industry because it had been unthinkable that such a major character would die. Secondly it was drawn in a way that suggested Spidey may have been responsible for her death, because her neck snapped back when he stopped her fall with his web. This story is often credited as the moment when the "silver age" ended and comics started to move to a new era, dubbed the "bronze age," with more adult themes and stories that had consequences.

In Green Lantern 76 (1970), GL was confronted by a an African American who said;
"I been readin' about you…how you work for the blue skins…and how on a planet someplace you helped out the orange skins….and you done considerable for the purple skins. Only there's skins you never bothered with…the black skins. I want to know how come?"
Race played out in other stories as well, as Luke Cage appeared in 1972 -following the Falcon in 1969- as an African American superhero, and one who was grounded in New York crime fighting of the 70's. Many of these stories also bear the fingerprints of Denny O'Neil (he wrote the Speedy storyline, he wrote that Green Lantern issue, he was an editor at Marvel in the late 70's as these more grounded tales began to emerge.) O'Neil played a key part in getting many of the CCA rules relaxed as the 70's wore on, which was another reason why this new breed of story was starting to come through.
These stories were there, but they were mixed in with lighter fare on the newsstands. And those newsstands were another aspect of the change; as the industry moved to the direct market and into dedicated comic shops, they found it easier to tell long form stories and to tackle darker themes. The move into the direct market would later come back to bite them but that was a long way off. The political, economic and cultural shifts of the 80's bled through into comics as with everything else. Miller was a part of that movement rather than the cause of it.
And that brings me to the third figure who needs to be mentioned in any history of the changes in comics. Alan Moore.
Moore played a much bigger part in the changing of DC, with his work on SWAMP THING and then with WATCHMEN. On SWAMP THING he completely re-wired the protagonist and elevated the level of storytelling from pulp to art , as well as creating a new supporting character by the name of John Constantine. He wrote THE KILLING JOKE which was one of the other main influences on Nolan's THE DARK KNIGHT. The success of Moore opened the door to other Brits like Neil Gaiman and Grant Morrison, whose SANDMAN and ANIMAL MAN books respectively helped created a whole new leg of DC's business, the VERTIGO imprint, which saw titles like PREACHER dominate the 90's. Morrison wrote ARKHAM ASYLUM, which is still possibly the darkest and most challenging take on Batman. Moore's influence is still felt; a throwaway GREEN LANTERN story he wrote in the 80's was expanded into THE SINESTRO WAR and BLACKEST NIGHT, two of the biggest "space opera" superhero events of the last few years, both were a lot of fun. He was also fond of pointing out the basic silliness of superheroes. So modern DC is really the house that Alan Moore built. (It's nice to see them treat him with such respect.)
Another aside here I should mention is that while I'm crediting Alan Moore for creating and influencing everything in the known world ever, It would be criminal not to mention a title that came at around the same time. MAUS by Art Spiegelman wasn't a superhero book, so it's never quite gotten the press of WATCHMEN or TDKR, but it told the story of the Holocaust, drawing on Spiegelman's own family stories, and presented the characters as animals (Jews being mice and Germans being cats.) It was an amazing work that showed what the medium could do, and deserves to be on all of you shelves along with WATCHMEN. Maybe put it in that space that you free up by throwing out TDKR.
Miller's big impact was on DAREDEVIL, a title he started to work on in 1979. That's where he put his stamp on the super hero comics from a content point of view. Many of the things that people credit him for doing with Batman are actually things he did with Daredevil. He took a C-List Spidey knock off and turned him into a compelling and tortured hero (much of this run on the book was edited by some fella named Dennis O'Neil). He added in elements of Film Noir and Greek tragedy, with a healthy dose of what would later become an unhealthy ninja fixation, before ending his time at Marvel with the truly amazing DAREDEVIL: BORN AGAIN. He challenged tropes and stereotypes of the super hero genre, but really was challenging them by adding in tropes and stereotypes of other genres. He was essentially creating a mash-up. And he did bring more violence to Daredevil, including one not-so-subtle image of Elektra being run through with a knife by bullseye, that was his 'look at me' way of depicting a rape murder under the watchful eye of the CCA. It was that work that got him noticed by DC, and that calling card that gave him the clout to play around with Batman. His twin great stories of DAREDEVIL; BORN AGAIN and BATMAN; YEAR ONE remain high watermarks in super hero storytelling, and it's worth noticing that in both, the protagonist spends most of the story out of costume. (One of the many problems I had with The Dark Knight Rises is that the film had very effectively argued that people don't need to wear masks to be heroes, before then shoving one of those unmasked heroes into the Bat-Cave at the end.)

The darkest and most violent era of superhero comics came in a spell between around 1994 and 1998. That was the period when many characters were killed off or crippled, to be replacement with new younger and more violent versions, new costumes involving guns and armour and women in fridges. This was a poor period creatively and politically, but can't be laid at the feet of either Frank Miller or Alan Moore. Both of them by this point had left mainstream comics for the smaller companies that gave them more control and freedom. The result from Miller was the (infinitely silly) SIN CITY series. Moore was by this intent on showing that WATCHMEN hadn't been the only thing worth saying, and was bringing the fun and silliness back to comics with work on SUPREME and TOM STRONG. He had also spent some time being more overtly political, with the publication of AARGH (Artists Against Rampant Government Homophobia) and began the project LOST GIRLS which was aimed at reclaiming erotica and pornography as healthy art.
So if Miller was done with superheroes, and Moore was at work embracing the silliness that had always been a hallmark of them, where was the violence and darkness creeping in from? The real agents of change were pop-culture and movies. Batman, essentially, had the same problem as James Bond. In the 80's he'd found himself competing competing with a new breed of both writer and hero. The action films of Arnie, Stallone and Bruce Willis scared the hell out of the Bond producers and set in an identity crisis that it took a generation to solve, and the same cultural shift hit comic books. As films were filled with larger spectacles and more violent heroes, comic books tried to follow the shift to keep readers. The direct market was becoming a large cause of this; when comics had been on the newsstands there had been a new generation of young fans every few years, but with the product becoming confined to specialist shops the audience was growing older and not changing, and so the industry tried to compete with that this ageing audience was watching.
And for awhile it worked. The industry had a major boom in the mid-90's and issues were selling at a rate that they've never matched. But for every new fan who came in from the mainstream media attention, there were more who were leaving because of the changes. Some characters have managed to come back and find their feet, others have remained stuck in that time, reeling from a change they couldn't cope with.
But the good news was that the industry found a new generation of young writers who were coming through with a love of all the different eras and could combine them. We had James Robinson's STARMAN, which was a love letter to both silver age and modern age super hero stories, and then following on later writers like Brian Bendis, Ed Brubaker and Geoff Johns, who each combined all of the genres past into successful mainstream stories.
These days there is a comic book to suit everybody. Batman is a great example; you can find the grim and moody vigilante, you can find the action hero, you can find the caped crusader. Whatever you want, you cant find it. (Well, unless you're a woman or one of the many ethnic groups still marginalised, but even there, the industry is better than ever, it's just not good ENOUGH) There is a good varieties of tone and pacing, light and dark, but in a critically shrinking marketplace (though this has been a good year for sales so far, with smaller companies gaining ground on the big two). For people wanting a simple romp of a story I can recommend the new ROCKETEER series that has just launched at IDW, for the darker and more coldly logical end of the tights'n'capes thing I would suggest Irredeemable from Boom! Studios. Both of these are written by the same writer, which shows how interesting and open things are now.
Creators are starting to have to fight to be heard, but are also fighting for ownership of their own characters, which will free them up long term from the kind of editorial and corporate mandates that drive the likes of Batman and Superman. It'll be interesting to see what the costumed heroes are like in ten years time, and how the industry will support them. I'm not sure If I'll still be reading about them at that point, because my tastes have moved further and further away from men in tights and masks who name themselves after animals, but hopefully they'll be in a place where Miller can't keep claiming credit for things he didn't do, while Alan Moore sits in a house in Northampton wishing people would stop trying to talk to him about an industry he revolutionised thirty years ago.