Maybe I should have called this 'The Many Faces of Batman' to prevent confusion? Because this has nothing to do with Two-Face. Like, at all.
Batman is probably one of the most written fictional characters in history. As of right now, something like a quarter of the titles DC publishes in any given month have something to do with Gotham City and the Caped Crusader. He's been running in continuous publication for 75 years with multiple titles. He's been featured in 8 live action films and a number TV shows.
His enduring popularity - which has been skyrocketing in recent years - has to be for something. There are critics I respect immensely who argue that Batman's popularity stems from his most toxic elements, the angry juvenile vigilante fantasy. To be frank, there's a degree to which I definitely believe that's true. Fandom can be an ugly, angry place.
But I also think there's a lot more to Batman than that. And I don't think any creator I've read has realized it as brilliantly (or as explicitly) as Warren Ellis did in his brief Planetary/Batman crossover, "Night on Earth." "Night on Earth" is typically remembered for its fun metatextual gimmick that finds us cycling through Batmen from years past, from the campy Batman of Adam West's legendary TV show...
... to the gritty urban warrior of Frank Miller.
But people often don't talk about the finale of the book. That makes sense; the reality-hopping antics in which various versions of Batman faces off against Planetary are handily the 'coolest' parts, and the easiest way to sell the material to people. But they aren't the point, they aren't what Ellis was trying to say. The reason the story endures to this day (is anyone still talking about Spawn/Batman?) is because of this finale.
To give you a quick recap, John Black is a killer - but he's a killer with the ability to jump from dimension to dimension. An ability he can't control. When the Planetary team hunts him down in the Wildstorm version of Gotham City (which finds Dick Grayson and the Joker running the local Planetary offices together, and no Batman), they find themselves chasing Black from dimension to dimension, where they learn that in many worlds, Gotham City is a little bit more... interesting. As they jump, they encounter and clash with Batman in a number of different forms as each side pursues Black for their own ends.
As a quick note, from here on out, I'll be discussing the conclusion of "Night on Earth" extensively, so for the spoiler-averse... you've been warned.
It is here that we see, on a fundamental level, the reason Batman works. Typically, when we talk about why people love Batman, we focus on the tangible details. Sure, he's got a cool costume. Yeah, he's got iconic villains. He's bad-ass, but he, like, doesn't have superpowers maaaaaan, but he could totally beat Superman (somehow). But there have been literally hundreds of those characters created in the years since - and none of those tangible details, not the Batmobile-tank, not the Batswords or the Anti-Female-Villain-Repellant Bat Spray, not even a gun could stop John Black.
It's worth noting how expertly this transition took place. You see, prior to now, the middle-third of the book was dedicated to the most indulgent aspects of the Batman mythos. The cool costumes, the gadgets, fighting a superhuman to a standstill - it was all the things people love about Batman, with a cool gimmick binding them all together. The issue probably could have concluded in that vein, and fans probably would have been reasonably satisfied. No one would particularly remember it, but it would have been fine.
Instead, as the story nears its conclusion, things... shift. John Cassaday, who illustrates the issue, had been changing the tone of the work on the fly, modifying the colors and designs slightly to hearken back to a particular era. Eventually, however, we return to the Bob Kane/Bill Finger era of the character and then beyond. It is this final Batman, something of an amalgam of the ones that came before, that is most important. It is only then, once we've dug through every major incarnation the character has had and discarded all the chaff that's accumulated through the years, that the Planetary team and John Black learn of his origin.
Like the now-iconic opening page of All-Star Superman, they spend only a single page recapping his origin... but this origin comes 90% of the way through the book. Why put the origin here? Why retell the origin at all?
Cassaday illustrates the sequence starkly, no words and minimal color. He focuses on a young Bruce Wayne, lit almost with dramatic stage lighting, reliving the moment for the thousandth time - with John Black curled up in agony in front of him. And that, I think, is the important part. The reason for the entire sequence, the reason for the run through Batman's history. This is the defining moment in Batman's character. Reminding us of Batman's loss reminds us of John's loss; it humanizes both of them, and takes the struggle from external ("We must stop him from killing again!") to internal ("He'll stop once he comes to terms with his parents' deaths.")
I've seen many people talk about the mutability of Batman, who has been a vigilante, a fascist thug, a master tactician, a detective, an inventor, a deputized law officer, and there are fans and critics who have named pretty much every single one of those things as 'the essential trait of Batman'. But that's not it at all. The essential trait of Batman, the only trait that must be maintained, is loss, and what that loss drove him to become.
It is that loss that allows Batman to connect to John Black (and the Robins... and Superman... and us). And, ultimately, it is that bond - the bond between two people who lost everything and have tried desperately not to lose themselves in response - that saves the day. There are two faces to Batman in Planetary/Batman: Night on Earth - and, in many ways, in every Batman story, good and bad. The first is all the cool stuff. It's fun to watch, but it doesn't actually accomplish anything - indeed, in the story, it actually makes the situation worse, triggering John to shift worlds faster and faster, with less and less control. The second? It's the human stuff - and only that little bit of empathy buried in years of accumulated ephemera can defeat the villain.
At his best, Batman is an aspirational figure. Someone who protects the most helpless members of society because no one protected him when he was helpless, someone who seeks to bring order to a fundamentally chaotic world. Modern writers have positited his quest as one to 'cure' Gotham, but I think that's a mistake. It's a winnable quest that comics will never let him win, which makes him seem incompetent or Gotham seem supernaturally cursed. Planetary/Batman suggests a different type of quest: To prevent more people from going through what he did. It's a quest no one could ever win, and thus there is nobility in his striving, a modern day Don Quixote. He remains a fundamentally irrational figure - it takes an awful lot of steps to go from "parents shot" to "dress like a bat and fight crime" - but that irrationality gives us a lot of empathy for his impossible quest.
At his worst, Batman can an indulgent mess of a character that glorifies our worst impulses. He can be a brutal, hyper-conservative thug. He is, to paraphrase a famous description of the character, a wealthy white man beating up the mentally ill. He's someone you want to be because everyone wants to be the toughest, the coolest, the least able to be hurt.
Batman is a figure I have a hard time loving unconditionally because of that. But every so often, a writer like Alan Moore, Grant Morrison, and, yes, even noted cynics like Warren Ellis or (once upon a time) Frank Miller will come along and find the beating human heart beneath the psychoses. These are the stories that make you love a character, that make a character last. It doesn't matter how 'cool' a character is, or how bad-ass their rogues gallery. Even in a story that's the absolute height of cynical cash grabs - the franchise-driven crossover - that one truth lead "Night on Earth" to become one of the best Batman stories out there. Because empathy is everything.
Anything else is just window dressing.