The Dark Knight Strikes Again is a disaster of a comic. It has about as much subtlety and nuance of... Well, any other latter day Frank Miller comic. Pick your poison. Like a lot of dumpster-grade creative works, however, what it has in spades are the kernels of good ideas. Take its interpretation of the Joker, for instance.
Now, if you've read the book's precursor -- the seminal The Dark Knight Returns -- and nothing else you might be wondering how there even is a Joker.
The clown that doesn't frown offed himself at the end of the previous story, leaving his longtime nemesis/best friend Batman in a bit of a pickle. What with framing him for his murder and all, after the decrepit Bruce Wayne chose one final time not to kill him.
Yet he returns, amid a cavalcade of unrelated baddies and under the veneer of Miller's slapdash art. Except this Joker isn't the one Bruce fought for all those years and decades beforehand. Instead, it's one of the Dark Knight's oldest and only friends. One Dick Grayson, a.k.a. the first Robin.
It seems in this continuity Bats gave Dick the boot for being too incompetent. This being after the boy in black drafted young Robin into his war on crime, questioned his mental faculties, and admitted even to himself that the kid was too traumatized by the death of his parents to be drawn into the dynamic duo. The Batman of Earth-31 (Miller's universe) is pretty awful, if you hadn't noticed.
And so Dick rightly developed a dislike for his former boss. So much so that he opted into an experiment that made him a nigh immortal shape-shifter.
The trade-off supposedly being that it also unbalanced him psychologically, though we'd guess that Batman's abuse had a part to play in that long beforehand. These issues drove him to torture Bruce right back by becoming the second Joker, then murdering several superheroes to draw his old mentor out.
What's really tragic about this version of the villain is what it says about Dick. In most other comics, Grayson is just about the most well-adjusted individual within Batman's pull -- second only maybe to Barbara Gordon. Batgirl, for the uninitiated. He's kind, funny, likeable, and on the rare occasions that he had to don the ears and cape just as capable of pulling off the Batman gig as his mentor. For him to wind up this bad his world and so-called father figure must have really, truly done a number on him.
The Joker of Batman: The Animated Series and its subsequent spin-offs was typically pretty tame. Despite some rather upsetting imagery from time to time, this iteration of the clown prince was intended for children, after all. As time went on, however, the animated universe began to edge closer and closer to the edge of "family friendly."
One such step forward was Batman Beyond. Set 30-some years after the original series we got ourselves a new Batman, a cantankerous Bruce Wayne, and a lot of weirdly effective cyberpunk plotlines. Not to mention one very messed up conclusion to the otherwise mostly amicable Joker.
In this version of events, Joker pulls A Death in the Family on third Robin Tim Drake (instead of Jason Todd). By which we mean he tortured, disfigured, and otherwise tormented the kid until he snapped.
At this point Drake snitched on his boss, and joined forces with the Joker. Though not exactly in a stable frame of mind. In fact, when Batman comes to his sidekick's aid, Tim snaps out of his brainwashing just long enough to blow Mr. J away. With a spear gun.
Though unfortunately it didn't even end there.
Jump cut to those 30-ish years later. The Joker is back, and he's still using Tim Drake for his not-so-funny antics. If abusing the young Robin psychologically wasn't enough the Joker literally got inside his head. This time with a microchip that implanted his thoughts, memories, and personality. The Joker being the Joker, he made sure that even after Tim escaped his abuser -- and the memories thereof -- he wouldn't be safe forever.
This was far from the first time the animated Joker pulled some dark shit (check out Mask of the Phantasm for more on that). It did, however, lead to some of the most overtly horrific scenes in the cartoon's existence. Not to mention one of the Joker's more altogether twisted moments in the DC multiverse.