“We aren’t contractually tied down to rationality! There is no sanity clause!” So says the Joker in The Killing Joke, Alan Moore’s graphic novel deep-dive into the psyche of Batman’s oldest and most demented enemy.

It’s a sinister twist on the Marx Brothers joke, but just scratches the surface of the Joker’s twisted mix of humour and sadism. For more than 75 years he has been the darker shadow behind the Dark Knight, the twisted yin to his implacable yang.

This week it was confirmed that Joaquin Phoenix would be the fourth big-screen, live-action Joker in a Todd Phillips-directed "gritty character study" set to be released in October 2019. Phoenix has swiftly snatched the role from Oscar winner Jared Leto, who tackled the role in David Ayer’s Suicide Squad. While the finished film didn't feature as much Joker as many fans were expecting , most of the press coverage around Suicide Squad's 2016 release was dominated by Leto’s attempts to get into character as the demented villain.

He apparently refused to break character and claims to have sent castmates live rats, bullets, used condoms and anal beads in an attempt to unsettle everyone around him. The actress Rose McGowan was so disgusted by all this she took to social media, urging his colleagues to sue: “In what other industry would this be sanctioned?” she wrote. “It's not something to be celebrated, it's something to sue over.”