Batman's greatest villain has been Joker for longer than anyone else in the Caped Crusader's rogues gallery. He was the first genuine supervillain Batman ever faced in comic books after a year of fighting crime lords and mafia in Detective Comics. The two have had over 80 years to make life hard for each other.
Batman has his no-kill rule and always works to put Joker behind bars for his crimes time and time again. However, there are moments when Joker has pushed the limits and made it hard for Batman to hold back. Joker has brutalized Batman, killed close companions, and committed crimes that prove there will be no redemption for the Clown Prince of Crime.
Joker Killed Robin
Easily, the worst thing that Joker ever did to Batman was kill Robin. One thing that Batman has always done was take in young teenagers and give them a chance to become a hero under the Robin mantle. After Dick Grayson graduated from the role and became Nightwing, Batman found his second Robin in Jason Todd.
However, his fate was sealed when he ended up on the wrong side of a Joker crowbar. Joker has always felt Batman was weaker with Robin by his side, so he murdered the teenage Robin and devastated Batman for many years. Joker did pay for this when Jason returned from the dead and became Red Hood.
Joker Framed Batman For Killing Him
Joker and Batman have a weird dance that they have pulled off for years. Joker torments Batman and kills numerous people, but he knows Batman will never kill him and he will just eventually break out of Arkham Asylum and the dance will start again. However, there was a time when Joker realized it had come to an end.
In The Dark Knight Returns, Batman had retired and Joker stayed in Arkham Asylum. When Batman returned to save Gotham City again, Joker also returned. This ended with the ultimate win for Joker. With the police looking on, Joker broke his own neck and made it look like Batman was who killed him, setting the police after Batman to finally stop him.
Joker Turned Everyone Against Batman
In the 2014 storyline Batman: Endgame, Joker was in the middle of a giant plan to destroy Batman - and specifically how people looked at him. He has already messed with Batman's allies in Death of the Family, and here he set Batman off into a fight with the regular citizens of Gotham City, as well as the Justice League.
Joker released an airborne disease in Gotham City that turned everyone it infected into a raging Joker-like villain, all intent on killing Batman. He then infected the Justice League and they went after Batman as well. This was Batman vs. the world, and it was all Joker's fault.
Joker Turned Superman Against Batman
One of the most shocking moments in history came in a comic book that was also adapted from a popular video game. This was Injustice: Gods Among Us. This was a fighting game similar to Mortal Kombat, but the people fighting were DC heroes and villains. The explanation of why Superman turned evil in the game was shown in the comics.
Joker had mixed kryptonite with Scarecrow's fear gas and dosed Superman with it. This caused Superman to think Doomsday had attacked and he flew the monster into space. However, it wasn't Doomsday - it was his pregnant wife Lois Lane, who died. As Batman watched in horror, Superman killed Joker in cold blood and then took over the world.
Tormented Jim Gordon
One of the people that Batman trusts over all others is Commissioner Jim Gordon. As Year One showed, Batman and Gordon arrived in Gotham at the same time, with Batman growing into the city's protector and Gordon eventually becoming the commissioner. They had each other's backs the entire way.
That made Joker's infatuation with Gordon so damaging to Batman. Joker shot and paralyzed Barbara Gordon, stripping the world of Batgirl. He also murdered Gordon's wife Sarah during the events of No Man's Land. Batman had to stop Gordon from stepping over the line both times.
Death Of The Family
Death in the Family was where Joker killed Robin and destroyed Batman. In the New 52, DC presented Death of the Family, which saw Joker try to destroy the entire Bat-Family. He targeted each of Batman's allies, one by one, including Robin, Red Robin, Red Hood, Batgirl, and even Alfred Pennyworth.
Joker claimed that he needed Batman to be at his best while they feuded, and caring about all the Bat-Family only made him weak. Eventually, Joker fed Alfred this poison gas and forced him to help torment the other Bat-Family before Batman finally stopped him.
Infecting Damian Wayne With Joker Venom
Joker killed Jason Todd, which devastated Batman. However, when Joker targeted Damian Wayne years later, it took it a step too far. While Batman took in Jason and helped him, Damian was his son. That made Joker infecting him with Joker Venom one of the worst things he ever did to Batman.
After Joker infected Damian, he sent him to fight his own father to the death. Batman, also infected, began to battle his own son. What was the worst moment about all this is that Damian said he would rather die than kill his father, and that is when Joker executed a failsafe to end the fight.
Emperor Joker
The Joker story in Emperor Joker is more connected to Superman than Batman, but that didn't stop Joker from making Batman's life a living hell. In this story, Joker stole 99% of the reality-warping powers from the Superman villain Mister Mxyzptlk. This made Joker pretty much omnipotent.
While this is based on a Superman villain, Joker decided he wanted to use his godlike powers to have some fun. He became Emperor Joker and realized he could kill and resurrect Batman. As a result, he tortured and killed Batman every day, and then brought him back the next day to do it again in a different manner.
Joker Killed Robin And Batgirl In Front Of Batman
In the Elseworlds story, JLA: The Nail, the world looked very different. Jonathan and Martha Kent never found Kal-El, so Superman ever existed. Instead, the Kryptonian tech was sold off to criminals to use in any way that they wanted. One of these was Joker.
Joker used the Kryptonian gauntlets to take over Arkham Asylum. He had the inmates fight to the death for his own amusement. He then trapped Batman in the Asylum, using the tech to not allow him to move. When Batgirl and Robin showed up to help, Joker used the gauntlets to tear them apart in front of a helpless Batman and then just quipped that at least they weren't screaming anymore.
Joker Created Batman Who Laughs
Dark Knights: Metal is a case where Joker did something nice to help Batman and save the world. However, the twist is that by doing so, he was able to hurt Batman - or at least a variant of Batman. This storyline introduced the world to The Batman Who Laughs, who was Bruce Wayne from another Earth.
Joker had laced his own heart with a device that would out some Joker Toxins when he died, so even after his death, his killer would become the next Joker. This was Batman, who ended up killing all the heroes on his Earth and then set out to do the same to this world. This world's Batman went to Joker for help, since his unpredictability gave him an advantage. One Joker drove Batman to evil and another helped defeat him.
