The Joker has never had a definitive origin story.

Its absence is a defining characteristic and, arguably, never really needed to be explored. However, when Joker draws to a close and the titular villain lets out his last laugh you will be pleased that Todd Phillips has done so.

Drawing from elements of Alan Moore's The Killing Joke the film follows unsuccessful clown and stand-up comedian Arthur Fleck's (Joaquin Phoenix) descent into madness as a series of violent events kick-starts his transformation into The Joker.

With few special effects and large-scale set-pieces on display, Phillips' film has more in common with the bleak, slow-burn character studies of 1970s and 1980s cinema - especially Martin Scorsese's Taxi Driver and The King of Comedy- than with its more action-fuelled, though equally effective, comic book counterparts.

It's a grim, rat infested world we are presented with and it serves as the perfect setting for Arthur's fall.

Rake-thin and plagued with a haunting pathological laugh, Phoenix is astonishing in the title role, giving a tortured, physical performance that is at once sympathetic and, as Arthur's actions become more monstrous, deeply unnerving.

While this transformation is compelling, Arthur's mistreatment and his subsequent actions often make for upsetting viewing, but in many ways it should be so; for this the origin story not of a hero but of a villain.

It is not always subtle - some reveals are delivered in sledgehammer heavy fashion- but this is a dark and bold reimagining of the genre and a considerable cinematic achievement.