The Joker was one of DC's most depraved and sadistic enemies, frequently associated with the Dark Knight as his most iconic villain. Such a comparison is apt; the two are a virtually perfect antithesis of one another, a fact that each of them has commented on in at different points of their escalating rivalry.
Though there have been some that claim there is good in the Joker, his monstrous actions indicate otherwise. By identifying the Clown Prince's most heinous actions, we have a better understanding of the incorrigible monster he actually is.
10 Turning Robin Into A Joker
At the height of Batman's conflict with the Joker, he had abducted Robin and broken him to his will. The villain would accomplish this through a combination of chemicals and torture, cracking the young boy's mind until he was just as much of an empty husk as his tormentor.
After the Dark Knight had been defeated, the Joker ordered his apprentice to execute his former master. Though it seemed as if Robin would obey him, the new member of the Clown Prince's "family" would fire at his creator instead, putting him down once and for all.
9 Murdering Bonk
Though Tim Drake had allegedly "killed" the Joker, the villain lived on through a microchip planted on his body. Decades later, the notorious Clown Prince would resurface, claiming ownership over the current Jokerz Gang and using them in order to enact his will.
After a partially successful mission, Bonk—one of his henchmen and easily the most physically competent—challenged the leadership of the group's new master. The Joker immediately murdered him for this trespass, forcing Harley Quinn's own granddaughters to dispose of his corpse.
8 Crippling Barbara (And Torturing Jim Gordon)
In The Killing Joke, the Clown Prince had easily one of his most decisive and controversial victories. Surprising Barbara Gordon in her own home, he shot her point blank, paralyzing her from the waist down.
Subsequently, he would also capture Commissioner Gordon in the same mission, forcing him to attend his twisted carnival and to watch the pictures the villain took of his daughter "in a state of undress." Though it was unclear exactly how far the Joker took perhaps his most openly malevolent task, his ultimate aspiration to drive the police chief insane was a failure.
7 Kidnapping Lois Lane
During his unlikely partnership with Lex Luthor, the Joker kidnapped Lois Lane and used her to lure Superman to him. With a large chunk of kryptonite in his possession, he was able to weaken the Man of Steel and would have electrocuted him to death if Batman did not intervene.
However, the Joker was prepared for the Dark Knight and had contingencies. Noxious fumes filled the room, jeopardizing the Caped Crusader and forcing him to think on his feet in order to survive. It was a straightforward (albeit sinister) example of the Clown Prince's ingenuity, proving that even Superman is not completely invulnerable to the most twisted mind in the DC universe.
6 Throwing Harley Out Of A Tall Building
The relationship between Harley and the Joker has always been an abusive one. However, it found its climatic (and surprisingly heartbreaking) conclusion after Quinn had successfully captured Batman and offered him to her boyfriend.
To the astonishment of many, the Clown Prince so enraged by this that he threw her out of a tall building. It demonstrated just how little her life meant to him and the disturbing depths of his ego. He claimed that the Batman's demise had to be perfect, the punchline to a "joke" that she could never understand.
5 Trying To Get Batman Executed
Despite having nearly murdered Harley Quinn for attempting to dispose of Batman "improperly," the Joker had attempted to convince Lex that the Dark Knight must die when he was captured. Held in inescapable restraints, the Clown Prince had presumed it to be the perfect opportunity to finish off his timeless enemy.
Ever the pragmatist, Lex would decline this request on account of Batman's usefulness. Understanding the sentimentality behind the Justice League, he suspected that a hostage might come in handy if Superman were to gain the upper hand.
4 The Emperor Joker Arc
The Emperor Joker arc introduced a world where the Clown Prince had fathomless power. He had attained it through deceiving Mister Mxyzptlk—a jester strong enough to defeat Superman on his own merit—depriving him of almost all of his strength in the process.
What came next was a horrible series of atrocities that illuminated the darkest depths of the Joker's mind. He killed Batman dozens of times, turned Harley Quinn into a constellation, and unleashed many other gruesome afflictions against the unprepared denizens of the DC universe.
3 Creating Clayface
In 2004's The Batman, Clayface had a much different backstory than his canon counterpart. Policeman Ethan Bennett was captured by the Joker and subjected to his torments, gradually cracking his mind and changing him into the vicious villain that the Dark Knight would frequently battle against.
However, instead of being blatantly antagonistic, he served as an anti-hero for the series, going against Batman for the right to flagrantly kill the Joker (instead of merely arresting him). Though they may have been at odds after Clayface's initial transformation, the two men would eventually work together after Wayne's arduous attempts to facilitate his rehabilitation.
2 Creating The Red Hood
One of the Joker's most iconic sins was in his creation of the Red Hood. He had captured Jason Todd and beat him ruthlessly with a crowbar, absconding before Batman had arrived and set the warehouse to detonate.
Through the miracle of the Lazarus Pit, Jason Todd was reborn, donning a new cowl and mentality that would put him at odds with his former teacher. Though they occasionally assisted each other, their dramatically different philosophies saw the two men at one another's throat more often than not.
1 Getting Superman To Kill Lois Lane
In the Injustice arc, the Joker was able to deceive Superman into killing Lois Lane, who had been pregnant with their child. This set the Man of Steel into a brutal rage, one that would culminate with the Clown Prince's demise.
However, the Joker's death would only be the beginning of a new era. It motivated Superman to form the Regime and divided the hero world against itself. Many other characters would fall by his hand after the incident, even including Shazam. The Clown Prince had addled Clark's mind so irreparably that he would kill a child of his own free will.