There are a lot of clowns in the world, as it turns out, and they’re pretty protective of their appearances.

Perhaps surprisingly, copyright was the main challenge faced by the crew members tasked with creating the unique look for Joaquin Phoenix’s comedian-turned-criminal Arthur Fleck in director Todd Phillips’ hard-edged comic book movie Joker. Despite the best part of 60 years of comic book and big screen history and expectation, from the iconic purple suit and green hair of Cesar Romero through to the terrifying grunge of Heath Ledger, it was actually the risk of legal action from other, real-life clowns that presented the biggest challenge.

“We would often submit things to the legal department and they would say 'no, it looks too much like this, or this',” says costume designer Mark Bridges.

Make-up designer Nicki Ledermann shares his woes, adding: “There are so many different clowns and they're all under copyright and therefore we are not allowed to use them.”

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The process of Joker was always going to be iterative, say Bridges and Ledermann, finding the sweet spot between achieving a unique vision for arguably the most famous villain in comic book history, while also paying respect to the fans who know the actor better even than any warden at Arkham Asylum.

To the tune of more than a billion box office dollars — the most profitable comic book movie ever — they came through in a big way.

View photos Cinematographer Lawrence Sher, Joaquin Phoenix and director Todd Phillips on the set of 'Joker'. (Credit: Niko Tavernise/Warner Bros) More

More than most characters in gritty, violent dramas, Arthur Fleck and his criminal alter ego are make-up and costume-driven affairs. Ledermann concedes that this meant “the pressure was definitely on” when they started work on constructing the look for Phoenix.

She says: “You want to please everybody and you want to do something wonderful and unique. You don't want to fail because you don't want to let down your actor, your director or the other departments you collaborate so closely with.”

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Bridges says the design of any character “evolves” throughout the development process, with his original design for Arthur Fleck’s already iconic Joker coat taking a different shape to the one that was ultimately depicted on screen. He said his biggest headache was trying to create clown shoes for the early scenes in which Fleck portrays a jobbing clown called Happy.

View photos Joaquin Phoenix as Happy in Joker. (Warner Bros.) More

He says: “I knew he had to run after those kids at the beginning when they steal his sign and I was a little nervous about whether Joaquin would be able to run in these huge clown shoes. He used to take his shoes to choreography practice and work with them. He had an amazing stuntman too and they both learned how to run in the shoes.”

Phoenix was fortunately able to stay on his feet and the design of the Joker costume has quickly achieved a cult following, with it effectively becoming the costume of choice for this year’s Halloween festivities.