For the 2016 film, go here.
- Alternative Character Interpretation: Apart from the ancient "is Batman just as crazy as his enemies?" question, a growing number of reviewers in recent years have come to wonder whether the pre-Joker "Jack" - assuming the flashbacks are accurate - truly loved Jeannie as a person, or just an Extreme Doormat who'll put up with him no matter how nonfunctional he is as a breadwinner. Geoff Johns' Batman: Three Jokersnote made this explicit, positing that "Jack" was always abusive, and Batman/the police actually helped fake her death so she could escape him.
- Audience-Coloring Adaptation: Brian Bolland's interpretation of the Joker (very lanky, vaguely upward spiky hair, somewhat vampiric features) has dominated how the Joker has been drawn since the book came out.
- Broken Base:
- Arguably one of the most contested Batman stories ever written. There's many a debate over the merits of Barbara Gordon getting fridged and whether or not it actually lives up to the hype. For good or bad, it's become one of the most iconic and influential stories on the Batman Mythos, something that Alan Moore has actually come to regret.
- There is a long-standing debate over whether the original coloring or the deluxe edition coloring is better. The original coloring is bold and psychedelic, framing the story as a carnivalesque nightmare, while the deluxe edition is very cold, muted, and realistic. Some argue that the original colors were too garish for such a dark story and others argue that the new colors rob the book of its character and atmosphere by making everything so dim and washed-out. Other alterations like the removal of the yellow oval behind Batman's chest insignia and the addition of blood leaking out of the Joker's eyes in a certain scene incite even more debate. It doesn't help that the Deluxe Edition has since become the primary version of the comic since 2008 and is the basis used for the animated adaptation of the comic, all while the original comic has fallen into almost Keep Circulating the Tapes status (until it was re-released as part of Absolute Batman: The Killing Joke, which features both the original coloring and the deluxe coloring)
- Common Knowledge:
- Barbara Gordon was forced to retire the Batgirl identity after the events of this comic, right? Actually, she'd not appeared in comics as Batgirl for some time, and had already hung up her cowl shortly before this was released
- though DC being DC, this has been subject to numerous Retcons, and most modern writers seem to agree that she was still active as Batgirl the night she was shot. Adaptations like Batman: Arkham Knight and the 2016 movie also seem to take her still being Batgirl for granted. - Everyone knows that the Red Hood tripped on his cape and accidentally fell into a vat of chemicals, especially with so many adaptations replicating this scene over and over. Except no, the Red Hood didn't accidentally fell into a vat of chemicals. He deliberately jumped into the vat out of fear◊. This is actually staying true to the original Silver Age backstory of the Joker, where he clearly dove into the vat to escape Batman◊. The detail of the Red Hood accidentally falling in most likely came from Batman (1989), which was the first major adaptation to depict Joker's chemical bath origins, albeit as the gangster Jack Napier rather than the Red Hood.
- It's commonly claimed that the Red Hood fell into a vat of acid and became the Joker. In actuality, (as stated above) he just jumps into a vat of unknown chemicals. This misconception is likely due to a side comment in Batman (1989) where a character mentions Jack Napier falling specifically into acid.
- Barbara Gordon was forced to retire the Batgirl identity after the events of this comic, right? Actually, she'd not appeared in comics as Batgirl for some time, and had already hung up her cowl shortly before this was released
- Crosses the Line Twice: The Joker shooting Barbara in the spine is horrifying. The jokes he makes over her body are hysterical.
- Draco in Leather Pants: Many people run with the Joker and his characterization as a victim in this story. This is ignoring the fact that he's probably making up his Dark and Troubled Past, as Joker admits he'd prefer to have his past be "multiple choice" during his Motive Rant (and Three Jokers reveals he was actually an Abusive Boyfriend to his wife, who faked her death to get away from him) . Also, the moral of the comic is that one bad day doesn't drive a person to madness, despite what the Joker repeatedly insists; the comic makes the point that Joker is responsible for his own actions, in spite of his "one bad day" that even he admits he can't quite remember.
- Epileptic Trees: During a 2013 podcast with Kevin Smith, Grant Morrison argued that the end of The Killing Joke in fact has Batman killing Joker, carefully interpreting the panels as evidence. This is a very dark interpretation of the story that contradicts the mainline DC canon, and the script for the comic says Batman and Joker just collapse helplessly in laughter (and is also an odd interpretation for Morrison to have, as their run on Batman makes clear references to The Killing Joke in the prose story "The Clown at Midnight"). Alan Moore himself would debunk this theory in 2016, explaining that the two are simply "laughing over their preposterous situation".
- Genius Bonus: The "joke" Joker tells Batman at the end of the comic, featuring two people trying to escape an asylum, references the Prisoner's Dilemma: a situation where two agents can either work together for mutual reward or betray one another that can also serve each actor's individual interest. This is very fitting for the Batman-Joker conflict: working together or killing one another, the Joker can't trust that Batman wouldn't let him fall even if it would serve him.
- Hard-to-Adapt Work: This is likely why it took so long for there to be a film adaptation, as the comic is not only very short (being a single issue that is only 48 pages long), but is drawn and written in a way that could truly take advantage of the comic medium (which is a trademark of Alan Moore's work and is precisely one of the reasons why he is against adaptations of his work), making it incredibly hard to translate into film. When Warner Bros. did get around to adapting the story into an animated film, not only were numerous changes made to make the story work better in animation, but an entirely new prologue starring Barbara was added to make the story longer. These changes and the prologue, however, only cluttered and weakened the story in the opinions of both critics and fans.
- Harsher in Hindsight:
- When the failed comedian that would eventually become the Joker is slumped in a bar, a man who looks similar to the Joker can be seen maliciously smiling at him in the background. 30 years later it's revealed that there's at least 3 Jokers and this Joker is implied to be a product of the original.
- While the comic features a Jim Gordon who doesn't go crazy even after his daughter is maimed, Batman: The Animated Series would have a (dream) episode where Gordon does go mad with grief when his daughter is killed.
- Jerkass Woobie: This is one of the very few things in all Batman media that can make one feel sorry for The Joker, even after the horrible and nightmarishly evil things he's done this time. Especially the scene towards the end, when Batman chases him. The Joker's face as he asks "Why aren't you laughing?" just breaks one's heart. He may be a monster, but he's also a pitiful, broken wreck of a human being.
- Misaimed Fandom:
- There are those fans who, even if they think he is still a sociopath, believe the Joker when he says that one bad day is all it took to drive him over the edge (and by extension, that one bad day could drive anybody over the edge). Not only is this arguably disproved by the end of the story, since he fails to break Gordon, note it's suggested by Batman that his failure and behaviour mean that the Joker was not even right about himself, and by extension needed help long before his Trauma Conga Line. That's not even getting into his Multiple-Choice Past claims.Batman: So maybe ordinary people don't always crack. Maybe there isn't any need to crawl under a rock with all the other slimey things when trouble hits. Maybe it was just you, all the time!
- The larger point that Moore regrets is that his origin was intended to deepen and complicate the rivalry between Batman and the Joker, and humanize the Joker by giving him a sympathetic backstory. Instead all people take from the comic is the Joker can be even more violent and sociopathic while using Multiple-Choice Past as an excuse for readers to accept and tolerate him as an entertaining villain, and this paved the way for various later stories to try to top it with Joker committing ever more hideous atrocities with his usual Straw Nihilist spiel.
- There are those fans who, even if they think he is still a sociopath, believe the Joker when he says that one bad day is all it took to drive him over the edge (and by extension, that one bad day could drive anybody over the edge). Not only is this arguably disproved by the end of the story, since he fails to break Gordon, note it's suggested by Batman that his failure and behaviour mean that the Joker was not even right about himself, and by extension needed help long before his Trauma Conga Line. That's not even getting into his Multiple-Choice Past claims.
- Moral Event Horizon: What the Joker does to Barbara. Of all the crimes the Joker has committed - even the murder of Jason Todd - this one haunts the whole DC Universe.
- Never Live It Down: Poor Barbara. Most writers who use her just can't seem to look past that one hellish moment of her life. This image◊ proved to be the last straw for many fans.
- Once Original, Now Common:
- Was pretty extreme when it first came out, even after Watchmen and Batman: The Dark Knight Returns intensified the comic book medium. Nowadays, the whole attack-a-woman-to-spite-a-man plotline has been done to death, with stories like Identity Crisis (2004) and Injustice: Gods Among Us milking it dry.
- The Killing Joke was the first time Joker attacked someone close to Batman's personal life. Several months after the release of this comic, there was the famous A Death in the Family story that killed Jason Todd, and much later, No Man's Land where Sarah Essen Gordon was killed by the Joker. This trickled into adaptations, where in Tim Burton's Batman (1989) Joker is made into the thug who killed Bruce's parents, and killing Bruce's Love Interest in The Dark Knight and Batman: Arkham City, while his torture of Batman's ally into insanity became an element of Batman Beyond: Return of the Joker and Batman: Arkham Knight.
- Bruce Timm has even said that despite the book still getting a mature readers tag in reprints and the 20th anniversary special edition, times have changed and the animated adaptation could've possibly gotten a PG-13 rating before it was rated R.
- Protection from Editors: Alan Moore later came to regret his treatment of Barbara, stating that it was one time when he should have been reined in, but wasn't. Somewhat alarmingly, Moore described his editor's involvement as actually egging him on, infamously telling him to "cripple the bitch," as he recalled it.
- Signature Scene:
- The Joker shooting Barbara Gordon.
- Joker's "One bad day" speech. Alternatively, the ending with both Batman and Joker laughing at the latter's joke.
- Tear Jerker:
- Joker's monologue is probably the first time in his run that he's truly bared his soul, showing the Sad Clown he is behind his monstrosity: he can't see anything but the bad in the world, so he decided to find the humor in the horror, lest he break even worse than he already has. For all his Straw Nihilist talk, Joker's sick sense of humor is him trying to find at least something redeemable in what he considers a rotten world: unfortunately, that 'something' was 'humor at the expense of others'.
- The worst part about the monologue is Joker's face in the panel where he asks, "[W]hy can't you see the funny side? Why aren't you laughing?" It's a combination of sadness and confusion, as he genuinely cannot understand why and how Batman's "one bad day" (his parents' murder) didn't lead him to become as openly insane as the Joker himself, how he could possibly see Gotham, and the world, as still redeemable even after the trauma inflicted by society around him, and he (Joker) begins to wonder if he really is alone in his madness and, as Batman soon says to his face, everything wrong with him might be his own fault, not the world's.
- At the end, Batman sincerely offers Joker a chance at rehabilitation and the chance to heal from his madness. For a second, the Joker appears lucid and seems to consider it, but solemnly declines. "No. I'm sorry, but no. It's too late for that. Far too late."
- Joker's monologue is probably the first time in his run that he's truly bared his soul, showing the Sad Clown he is behind his monstrosity: he can't see anything but the bad in the world, so he decided to find the humor in the horror, lest he break even worse than he already has. For all his Straw Nihilist talk, Joker's sick sense of humor is him trying to find at least something redeemable in what he considers a rotten world: unfortunately, that 'something' was 'humor at the expense of others'.
- Values Dissonance: The story's moral core, at least in the most common interpretation, relies on a very black-and-white kind of thinking that basically goes "Killing (even somebody who's a clear-and-present danger to civilians) isn't "by the book" -> Not doing things by the book means you're insane -> Being insane means you're every bit as bad as the Joker". Which is pretty in-line with the unironically law-abiding Batman of the '40s-to-early-'80s, but significantly more dissonant with the line-crossing Dirty Harry-esque rebel that Frank Miller popularized.note
