The unfortunately named Humphry Dumpler has suffered throughout most of his life from a string of almost supernaturally bad luck. A very large man with an egg-shaped head, Dumpler is compulsively driven to speak in rhyme and to disassemble then reassemble malfunctioning machinery in the hopes of fixing it. His criminal actions were not, therefore, intentionally malicious, but were instead misguided attempts to understand and "fix" the world that had so mistreated him. Nonetheless, his actions lead to various tragedies, such as the derailment of a train due to his inexpert reassembly. An attempt to fix the Gotham clock tower lead to a chain reaction of destruction that resulted in the deaths of several Gothamites. He also murdered and dissected his abusive grandmother, then sewed her back together with boot laces, again in an attempt to "fix" her.
He was incarcerated in Arkham Asylum not because he was a cruel or ill-intentioned man, but because his persistent tampering with machinery makes him a danger to those around him. He does not portray any of the common sadistic or evil traits usually common in Batman villains. In Arkham he was a model prisoner, often helping with minor repair tasks around the Asylum. He also befriended Warren White, later the Great White Shark, and even saved his life on one occasion.
He was a member of Alexander Luthor Jr.'s Secret Society of Super Villains during the Villains United storyline, and assisted in the attempt to retrieve the Get Out of Hell Free card from the Secret Six. He was recruited by the Black Mask to become one of the villains running Gotham during the Battle for the Cowl arc.
Humpty Dumpty is later seen dressed as Santa Claus. He is stranded in the cold while fixing his snowmobile until he meets Abuse, who is asking questions about runaway children that are turning up dead. Humpty Dumpty becomes distressed by Abuse's relentless interrogation so he grabs a crowbar and strikes him. Humpty Dumpty then breaks into a car, hot wires it, runs over Abuse and escapes.
Humpty heads toward an abandoned orphanage where the corpses of the runaway children reside. Humpty opens up a sack that is filled with toys and distributes them to all the children. Batman and Robin figure out Humpty's hideout after talking to the Broker. They question Humpty Dumpty’s scheme and they learn that Humpty simply wanted to give the children a proper Christmas. Dumpty informs the Dynamic Duo that Mr. Zsasz forces the children to engage in fights to the death and Humpty cleans up the mess. Dumpty tells the Dynamic Duo where Zsasz's underground arena is and Damian decides to compete in the arena in order to stop Zsasz's sick pleasure of watching children butcher each other.
When Hush reluctantly agreed to be Bruce Wayne, he had several inmates from Arkham and Blackgate put into a job placement program. For Humpty, he was given a place to stay in the Narrows and a job at a local bike shop where he could repair damaged bikes for customers. The job satisfied Humpty's compulsion to fix things but it still wasn't enough for him. On the eve of his birthday, Humpty invited fellow inmates who had escaped from Blackgate and Arkham to his birthday party. No one showed up except Joker with Two-Face strapped to a wheelchair. Joker presents Humpty with a sick idea for a birthday present.
Joker tells Humpty that Two-Face is still broken and needs to be fixed i.e. the other half of his face. Humpty becomes overwhelmed with anticipation and is overjoyed that Joker brought some tools to help with the procedure. Humpty starts off by cutting the right side of Harvey's face but Humpty complains that the knife is too dull and asks for some acid. Joker laughs at Humpty's eager persistence but he tells Humpty that an artist must take his time when making a piece of art. Fortunately, Harvey appeals to Humpty's psychological disposition.
Harvey tells Humpty that he gets his rocks off by finding things that are broken because he enjoys the torture he inflicts on his victims. Harvey continues provoking Humpty by saying he enjoyed killing his abusive grandmother and really had no intent in fixing her. Suddenly, Humpty bursts into a fit of rage by telling Harvey to shut up. Havrey finishes his little psychological warfare by saying the only person who needs fixing is Humpty himself. Humpty instantly becomes dumbfounded by an epiphany. He questions whether or not Harvey's conclusions are correct. Joker interjects by promising to fix Humpty himself. Humpty immediately considers himself so lucky to have someone like the Joker as a friend. Joker frees Two-Face and Harvey makes a speedy getaway while leaving Humpty at the mercy of Joker. Joker tells Humpty to sit down on a nearby coffee table and asks him he would "like to smile." Humpty's fate remains unknown but knowing the Joker, Humpty will continue living but only as something that the Joker would consider comical yet depraved.