He's the most popular comic book villain of all - which is perhaps surprising when you consider that the Joker, despite his penchant for comedy, has a truly black heart. There's nothing he won't do to torment Batman, no havoc he won't wreak on the streets of Gotham - with that in mind, let's take a look at the dark history of Batman's perpetual enemy ahead of his return in DC's Suicide Squad.
Who IS the Joker?
Comics are full of origin stories, but the Joker's origins remain somewhat unknown. He's been around for 75 years, and we don't even know his real name. In The Killing Joke, his appearance is explained by the suggestion that he fell in a vat of chemicals whilst on a criminal job which is interrupted by Batman, leaving him with bleach white skin and distinctive green hair.
However, being a pathological liar renders the Joker a classic unreliable narrator, and as he humorously declares in The Killing Joke regarding his own history: "Sometimes I remember it one way, sometimes another... if I'm going to have a past, I prefer it to be multiple choice!"
With no solid history and no grip on humanity, the Joker is free to behave in the most outrageous and brutal fashion - and if ever there was ever any good in him, it's long gone, as proven by a long history of diabolical deeds...
The time he murdered Robin
In A Death in the Family (Batman #426-429), Jason Todd (the second character to wear the Robin costume) tracks down his real mother, only for both to be taken hostage by the Joker. He murders mother and son before Batman arrives, too late to save his protege. The Batman comics have never shied away from cold-blooded brutality, and the Joker is consistently portrayed as true scum - despite which, audiences still love him. (In fact, this story arc was a result of DC polling over 10,000 fans, who voted by a slim minority for Jason Todd to die - perhaps the Joker was just being a good Samaritan.)
Darkness scale: 8 (because people actually wanted Robin dead)
The time he put Harley Quinn on a rocket
One of the Joker's most twisted relationships is that he shares with Harley Quinn. Despite their close relationship, the Joker attempts on numerous occasions to kill Quinn, although his motivations aren't always entirely bad - usually it's just because he's uncomfortable at how close they've become, and how the affection he feels toward her is difficult to reconcile with his deplorable personality.
Although that doesn't excuse the time he put her in a rocket which crash landed in Gotham. Or the time (in Batman #663) he enlists her to help carry out a bunch of murders, unaware that the plan will climax with her own death. Basically, it's not a healthy relationship.
In the trailer for DC's Suicide Squad (2016), we see the Joker (Jared Leto) appear to torture Quinn (Margot Robbie) whilst in a later timeframe Quinn and the Clown Prince go for a joyride with a certain caped crusader on their tales. Will the movie go as far as having the Joker orchestrate Harley's death, as he so often attempts in the comics? It remains to be seen...
Darkness scale: 9 (that's no way to treat a lady!)
The time he went on a mission to drive Commissioner Gordon insane in 'The Killing Joke'
So, we've pretty much established that the Joker is rotten to the core, but even the aforementioned antics can't match the events of The Killing Joke, in which he commits possibly his most evil crime of all.
In Alan Moore's iconic story, the Joker is on a mission to prove that even the man with the most sanity can lose it after a bad day. And the sanest man happens to be Commissioner Gordon. So what does do the Joker do to drive Gordon to the brink of insanity? He cripples Barbara Gordon, then shows the Commissioner photographs of his daughter stripped naked, possibly implying sexual assault.
Gordon still did not break, but the story was pivotal to the Joker's character in that it clearly demonstrated absolutely nothing is off limits. When Batman and the Joker come face to face at the end of the comic, Batman states that their game of cat and mouse will end with the death of one at the other's hands.
Darkness scale: a full 10
The trailer for Suicide Squad puts a pretty heavy focus on the relationship between Jared Leto's Joker and Harley Quinn, so we'll see just how dark this incarnation of the cruelest criminal in Gotham gets. If I had to guess, I'd say we're in for a lighter take on the Clown Prince, more comedian than devious killer. But the truth is, the badder his behaviour, the stronger our love for the Joker. He's the human embodiment of pure evil - and we wouldn't have it any other way.
Suicide Squad is released August 5, 2016.