It's only been a matter of days since the Joker movie hit screens, and already it's stirring up controversy.

The psychological thriller details the origin story of Batman's archnemesis, The Joker, and how he became the notorious villain he is.

But, while the eagerly-anticipated movie has been a huge hit so far, it hasn't been without its criticism, with many people calling out the film for its representation of mental illness - with some saying that it's so dark that people are walking out of theatres.

Keep scrolling to learn more about the "disturbing" movie and why so many viewers have been left unable to carry on watching.

He was most famously brought to life by Heath Ledger in 2008.

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The Dark Night was a box office smash hit, receiving rave reviews and grossing over a staggering $1 billion in revenue.

So, when it was annouced he was getting a movie of his own...

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...fans were elated. In fact, there was so much buzz around its release that the movie bagged the Golden Lion prize at the Venice Film Festival in September.

This time, the infamous criminal mastermind is portrayed by Joaquin Phoenix.

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Speaking to Ladbible, the Oscar-nominated actor explained: "I thought it was important for it to be its own thing, to be its own interpretation. What's interesting about this character is that everybody can interpret it however they want.

"Even with this film, I think the audience gets to interpret the character and what drives him, in a way that I think is unique for a lot of films. I mean it really asks the audience to participate, and I think that's interesting."

The movie hit screens last week.

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Directed by Todd Phillips, Joker tells the origin story of, you guessed it...the Joker (or Arthur Fleck as he's known as in the movie), and how he evolves into the criminal mastermind we all know him as.

Arthur Fleck is a lonely, failed comedian.

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Set in 1981, Fleck, who is working as a party clown, lives with his mother in Gotham City - a town full of crime and unemployment.

Fleck also has a neurological disorder that causes him to laugh at inappropriate times.

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Due to this, he often lands himself in bad situations. And of course, he finds himself on a huge downward spiral.

He becomes an outcast of society.

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Fleck is isolated, bullied, and lonely.

The movie chronicles his descent into madness.

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Soon enough, Fleck's life becomes rife with out-of-control into delusions, violence, and anarchy and thus, the clown-faced criminal is born.

The movie has solicited some extreme reactions.

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From rave reviews to full-blown outrage, the dark movie has debuted to extremely mixed emotions.

The movie has already broken a major record...

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Over the weekend alone it raked in an eye-watering $93.5 million at the US box office - although we aren't entirely surprised, given the huge anticipation in the lead up to its release.

But given its blatantly dark and, at times, sensitive themes, it was bound to whip up some kind of controversy.

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And it sure didn't disappoint, with many people slamming the movie for its representation of mental health and "glamorization" of violence.

Theatre-goers have also been left outraged by a particular song used in the movie...

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Convicted pedophile, Gary Glitter's 1972 "Rock and Roll Part 2" is used in one scene. Glitter was jailed in 2015 for a number of sexual assault offenses, including one count of raping a 13-year-old girl, so it's no wonder so many viewers were disgusted.

The movie is apparently so disturbing, it has been leaving viewers unable to continue watching.

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Several people took to Twitter to call out the "horrible" movie, saying how they've been left terrified while watching.