The Batman Who Laughs is a Multiversal version of Batman from Earth -22 of the Dark Multiverse.
The Batman Who Laughs is a Batman who exists on Earth -22. On this world, the Joker went overboard in his madness, murdering adults and infecting their now-orphaned children with Joker Toxin while a captured Batman watched. Infuriated, Batman broke free of his bonds and snapped the Joker's neck. However, killing the Joker caused a strange gas to escape from his mouth, Batman breathing it in.
The gas was another Joker Toxin, strong enough to infect someone and lasting just long enough to infect one person. Fully infected, Batman was transformed into a Joker-like madman who went on to destroy his world, a psychopath with one of the world's keenest minds.
The story of the Batman of Earth -22 was not much different from that of any other version of the Caped Crusader. However,
Joker learns of Batman's identity as Bruce Wayne and kills most of Batman's other rogues, along with Commissioner Gordon. He then subjects thousands of Gotham City’s citizens to the chemicals that transformed him,
everything went sideways when the Joker started a killing spree across the entire Gotham City, as he was dying from the same chemicals that had turned him into what he was. He murdered many of Batman's enemies including the Penguin, Catwoman, Killer Croc and the Ventriloquist. Batman was then drugged by the Joker, which only affected his body but not his mind, so he could witness the chaos his nemesis caused.
The Joker bombed a hospital in front of Bruce, told him that he had killed Jim Gordon by dumping him in a vat of acid and shot dead many parents of young children in front of him before proceeding to inject the children with the Joker Venom. Batman eventually broke free of his restraints and ended up beating and choking him to death in anger, repeatedly asking him to stop. Unbeknownst to him, the Joker had infected him too when he exhaled the Joker Toxin while dying. The children he infected had also acquired the Joker's personality.
Two days after the murder of the Joker, Batman and Superman talked about what had happened. Bruce revealed that Joker went as far as he did because he was dying. Though he felt no guilt, he affirmed that he was not planning to make killing a regular thing. Superman assured him that the S.T.A.R. Labs branch in Metropolis had agreed to take care of all the Jokarized kids.
A day later, Batgirl, Nightwing, Red Hood, and Red Robin were training in the Batcave when they noticed the training robots were fighting harder than usual. Though they succeeded at the exercise, Nightwing voiced what they were all feeling; something was wrong and Bruce brought them there to talk about it. Bruce explained that he had been infected by an advanced nanotoxin that had been contained in Joker's cell to turned the mind of anyone who killed him like that of his. Nightwing presumed he was training them so they could take him down in case he turned but declined, with the Batman Family pleading to let them help him. Batman, however, stated that he hadn't called them to help him, but to surprise them as he proceeded to shoot his sidekicks dead.
A week after the Joker's death, Bruce had slaughtered the rest of the Justice League by using the stockpiles of various villains' weaponry they had built up over the years. On the Justice League Watchtower, he cornered Superman and stated that he didn't want to hold back anymore. Clark warned him that people will resist him after realizing what he has become, Bruce responded that he looks forward to it otherwise it won't be fun. He then brought his wife Lois and Jon before him, the latter also suffering from bleeding eyes.
Bruce then mocked him and asked him to lie to his family that it will be okay, which Clark refused. He then unveiled a warped Damian and the rest of the Rabid Robins to Clark, before showing modified Black Kryptonite, stating that he tested it on Supergirl who killed her own foster parents before dying herself. Bruce's transformation into "The Batman Who Laughs" was finished, allowing him to cackle as Clark and Jon tore Lois apart before dying after he tossed the kryptonite towards them.
The people of Earth -22 fight back, but Bruce annihilated everything they threw at him until he and his Robins were all that remained. The last one to face him was Alfred, who almost managed to defeat Bruce by rigging his cave, his vehicles and all his equipment. But by convincing Alfred that there was still hope for him, Bruce managed to trap Alfred in sub-caves and by feeding him scraps and whispering to his ear all the time, Bruce managed to break Alfred to become his loyal servant again.
As his world began to fade from existence, Barbatos arrived and revealed the rest of the Dark Multiverse to him, and his plans to go after the true Multiverse as well. Believing him to be the ideal Bat to help him, he made him the spearhead for his plans to drag all of creation into darkness.
The Batman Who Laughs went out into the Dark Multiverse to assemble the most twisted versions of Batman out there to aid in conquering the main Multiverse. Travelling to each of the Knights' worlds minutes before they were erased from existence, he appealed to their desire not only to live but to bring their unique brands of truth and justice to worlds beyond their own. Each Batman jumped at the opportunity, and they awaited their moment to travel to Earth 0.
- Batman Who Laughs first appears in Metal Pt. I: Scarlet Speedster, mocking Red Death for his failure to defeat the player character and boasts about the Dark Knights' coming victory. His laugh completely freaks out Oracle.
- He next appears in Metal Pt. I: Monsters of Metal as the final boss. He takes on the players with assistance from Murder Machine's boom-tubed in Red Death, The Merciless and a swarm of Dark Robins. After the metal is delivered to the dimensional tuning rod, he reveals that everything the players have done was to his benefit and draws Earth into the Dark Multiverse.
- Batman Who Laughs is one of the possible mini-bosses in the first stage of the Metal Pt. II: Batscape 2 player operation.
- He is one of the Dark Knights in the final fight of the Metal Pt. II: Into the Dark Multiverse raid.
- The Batman Who Laughs first appeared in Dark Days: The Casting #1 (September, 2017)
- The Batman Who Laughs possesses a set of joker cards forged out of Cosmic Metallurgy; a material found in the Dark Multiverse that can manipulate reality to the holder's whim.
- The eyes of The Batman Who Laughs can see through the membrane of the Multiverse into the Dark Multiverse to see the things that people fear and desire. He uses a visor made of Dark Metal to filter out the dark energy and the noise in order to focus on what he wants to see.
- Each member of the Dark Knights represents one of Batman's worst fears and regrets. The Batman Who Laughs represents Batman's fear of becoming as bad as the Joker, how much he is defined by the never-ending war with the Clown Prince of Crime and his regret he cannot stop the Joker for good without killing him.