The latest Batman film, The Dark Knight, will inevitably make headlines, not least because the $100 million sequel to Batman Begins (2005) features the late Heath Ledger as the Joker. The director Christopher Nolan presents the Joker as an elemental force, a whirlwind of anarchy wreaking havoc on Gotham City. Ledger's character also lays down a challenge to Batman and attacks his psychological weakness, urging the Dark Knight to give in to his own darker urges.

Ledger died of an accidental prescription drug overdose in January, and he gives a memorable performance. Many critics believe he could win a posthumous Academy Award, for Best Supporting Actor (Peter Finch is the only posthumous winner so far, Best Actor for Network in 1977).

“I'm relieved that people are receiving the performance the way I know Heath intended it to be taken,” Nolan says. “My responsibility as a director has been in the edit room, to make sure that we were crafting the performance in the right way.”

In truth it is difficult not to respond to Ledger's performance. Christian Bale, who plays Batman for the second time, says that even his three-year-old daughter loves the Joker. “Now she's seen the trailer he's become a favourite. She says, 'Daddy, I like the bad guys!'”

Ledger crafts a complex character that - even though he's shorn of any back story and represents nothing but chaos and evil - is strangely likeable. Indeed, such was Ledger's affinity for the character that he contacted Nolan as soon as he found out that the Joker was going to feature in the film. His agent called the director and said that his client already had an idea of how to play the part.

“I met Heath several times over the years,” Nolan says, “and early on he told me that one of the things he was concerned about was not being thrust into the spotlight as a movie star before he'd shown what he could do as a serious actor. I've heard that from a lot of young actors but of all the people I'd heard it from, he was the only one I paid $10 to go and see deliver a crack performance. That was Brokeback Mountain. It's a performance of consummate skill. I think everyone recognises the great acting in it but what I think is easy to miss is the boldness of what Heath does with that film, because he plays an introverted character, a lonely character. He plays it with no thought of vanity, and he takes risks doing that. He's really throwing the net away.

“If there was anything surprising about him maybe it was how easy he was to work with,” Nolan continues. “Because he was somebody who put so much into his performances I was a little worried that he might take himself very seriously and all the rest. Yet he didn't.He was very warm and fun to have around, a great collaborator.”

Jack Nicholson's iconic Joker performance came in the 1989 film Batman, when Warner Bros brought the franchise back to the screen. It was directed by Tim Burton, with Michael Keaton in the starring role, as was Batman Returns three years later. When Joel Schumacher took over the director's chair - with Val Kilmer in the cowl and cape for Batman Forever (1995) and then George Clooney in Batman & Robin (1997) - the Bat-franchise began to lose its way; the latter was critically reviled.

The franchise then lay dormant for six years, until Nolan and the screenwriter David S. Goyer pitched the idea of a serious “origins” story, conjuring a darker vision of Batman that drew inspiration from the gritty world of the graphic novelist Alan Moore. “In many ways our film's not typical of a comic-book film and it has a lot in common with a crime movie,” Nolan says. “The film I reference a lot is Michael Mann's Heat, which is really the story of a city.”

Nolan's Gotham City is largely recreated in his hometown of Chicago. The 37-year-old director was born in London but his parents moved to the Windy City when he was a child. Like many men, he spent his younger years in the company of comic books and action figures. He had an army of plastic warriors drawn from the first Star Wars trilogy, including a model of Han Solo's ship, the Millennium Falcon, complete with smuggling compartments.

When he was 8, Nolan picked up his father's Super-8 camera and it wasn't long before his toy legions were starring in sci-fi productions, with the Falcon playing a key role in one particularly ambitious scene. “I stuck a banger in it and blew it to pieces,” he says.

Now he's at it again, although The Dark Knight's fireworks are detonated on a slightly larger scale - in one scene a 40ft truck is flipped end over end in the heart of the city's banking district.

Nolan's first feature film was Following, his 1996 debut shot for all of £3,000. Next came the cult hit Memento (2000), based on a short story by his younger brother, Jonathan, and then Insomnia (2002). All three, along with the subsequent Batman films and The Prestige in 2006 (which also starred Batman players Bale and Michael Caine), feature complex men torn between different aspects of their own personalities. “I'm not really conscious of that repetition,” Nolan says. “I try not to be too conscious about continuing things. I try not to worry about whether I'm repeating myself or whether it's going to be boring.”

Nolan remains tight-lipped on a third instalment in the franchise. “Which other Batman villains do I like?” He smiles. “I'm not sure I can tell you; I can see through your cunning ruse.” It seems likely that Warner Bros will be happy enough with the box office returns to commission a third movie.

The film should eclipse the $370 million taken by Batman Begins, Bale is signed up to a trilogy of films and Nolan clearly relished his latest challenge. Even when he was directing his smaller, independent movies, the director dreamt of making an intelligent blockbuster. He always wanted to blow up the Millennium Falcon, and he wanted to do it on a bigger stage.

The Dark Knight is released on July 24

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