Having removed his two-stone Batsuit for the day, Christian Bale slips into another, far more impenetrable suit. This is the invisible armour he wears to protect himself from the real world; a place where the villains are those who seek to unveil his true identity.
"An actor should never be larger than the film he's in," he states. True to his word, Bale continues to slip under the radar despite a career that began, aged 13, when he was cast in the lead role of Steven Spielberg's Empire of the Sun. In 2005's The Machinist, he lost more than four stone to play a troubled insomniac, but refused to discuss his weight-loss process for fear of trivialising the film's dark subject matter.
"Look," exclaims the 34-year-old Welsh-born actor, "I'm an actor, not a baby-kissing politician. I kick myself whenever I reveal too much about myself or my family. I don't view my personal life as some sort of gimmick to be used to promote a film."
In The Dark Knight, he reprises his Batman role alongside the late Heath Ledger's stunning performance as The Joker. Not that Bale is intimidated by competing with a more charismatic baddie. "Not at all. Because this is the problem I had with the other movies. I said, 'How come it's always been that Batman is the most boring character?' Whereas Frank Miller's Batman: Year 1 and other graphic novels depicted him as by far the most fascinating of them. I feel like we gained that back with Batman Begins. Of course he's a character who has substance and I have no problem with him competing with somebody else. So, I don't mind if everybody tries to chew up the scenery – which Heath certainly did.
"Our first scene was in an interrogation room, and I saw immediately that Heath was a helluva actor who totally got the tone that Chris [Nolan, the director] was trying to create. We're not going for actors revealing their enjoyment of playing a wacky caricature character; you go into character and you stay in the character. When Heath was in the make-up and the garb, he was in character the whole time and when he took it off, he was absolutely fantastic company to be around."
"In the movie, Batman starts beating The Joker and realises that this is not your ordinary foe. The more I beat him, the more he enjoys it; and Heath was kinda egging me on, going, 'Go on, go on, go on!' But he was slamming himself around, and there were tiled walls inside of that set which were cracked and dented. His commitment was total."
Eight years of marriage, to former model and make-up artist Sibi Blazic, has done little to soften Bale's intensity, although he allows himself a brief indulgence in discussing his youngest fan, three-year-old daughter Emmaline: "She loves the bad guys. Darth Vader is her absolute all-time favourite, although The Joker is fast becoming another. She even quotes him to me: 'Hit me!' and then looks all serious when she says, 'Daddy, I like the bad guys.' Now, she knows that I play Batman; what I don't know is if she truly understands I am just pretending to be Batman. I'm not looking forward to the day when she realises I'm just an actor who pretends to do that and, even worse, that stuntmen do the really dangerous stuff for me. I'm loving this age of absolute belief in me as a hero."
Bale signed up for three Batman movies. The first, Batman Begins, earned US$372m worldwide – a success of which he is both proud and relieved, having had his home repossessed five years ago. "I'm very proud of what we did with the first one. I was never really a fan of the previous Batman movies", says Bale.
Following Michael Keaton, Val Kilmer and George Clooney, Bale is the youngest ever actor to portray the caped crusader. But Bale was undaunted: "I really never think about other movies when I'm making a movie. I like remaining as oblivious as possible to it because I don't want to compare myself to other people. I would certainly never intentionally copy anybody.
"I think one of the nice things about Batman Begins and The Dark Knight is that a lot of people had written off the Batman franchise as a lightweight sort of thing, but we've got such great actors involved now in both movies," he says, unintentionally dismissing former Batman key-players like Jack Nicholson and Tommy Lee Jones. Bale particularly enjoyed his scenes in Batman Begins with Michael Caine: "What I learnt from Michael before I met him was 'Do nuffing'. He has an acting class on tape where he gives lots of pointers, including the advice, "Do nuffing." So whenever I get into trouble in a scene I always think: 'What would Michael do? Do nuffing!'
Although his predecessors complained about their bulky batsuits, Bale now wears a more flexible lightweight version, with a metal-mesh that enables the skin to breathe, and allows him to suit up in under 25 minutes. "The new suit is a lot better," he says. "I can actually turn my head and even sit in it for long periods of time without feeling that I'm gonna have rubber-suit rage. It's much cooler and more agile, whereas with the old one I was having to fight against the suit in order to do the moves I needed to do."
On the previous day's shooting in downtown Chicago, Bale had even insisted on performing a daring roof-top stunt that had been earmarked for his stunt-double. "That was a memorable day. It was planned as a good, nice shot of Batman looking out over the skyline. Overhearing somebody saying that they were doing it the next day, I said, 'No, I wanna do that. I want to stand up on the top of the Sears Tower.' I mean, wouldn't you, if you had the opportunity?"
If it seems like Bale is finally enjoying himself, then he refuses to be seduced by the easy life of your average Hollywood leading man. Still, he recently inked a deal to star as John Connor in the fourth instalment of The Terminator, the film franchise made famous by Arnold Schwarzenegger. "I still enjoy working in a variety of movies. To me the term 'challenging' tends to refer to when you're working with idiots and it's not going well. Then you're faced with the challenge of: 'Right. How do you try to make this work?'
"I like to think I can recognise those situations before going in, although I've certainly made errors in the past. But when you're working with good people, I pay little regard to the amount of effort required. If there's good people around you, I don't consider any role to be too difficult."
Bale has no desire to get behind the camera: "I just like doing what I do. I don't think I'd want the position of being responsible for other people, and having them ask me questions about how to do something. I think I'd be impatient, and tell them, 'Figure it out yourself, you idiot!' – you know? I think it takes a definite temperament to be able to direct and produce, and I prefer just being responsible for myself."
Asked if his new status as super-hero and highly paid Hollywood star has earned him more respect at home, he grimaces: "Maybe I live in denial, but I like to think I get a fair amount of respect the whole time. However, I'm unsure about the level of respect you can acquire when you go to work in a rubber suit, you know? It depends on how you look at it."
And depending on how you look at it, Bale may well be one of the most talented actor alive who can proudly say he's not a celebrity. "I'll take 'cult actor' any day over 'celebrity'," he says. "That's absolutely fine by me."
'The Dark Knight' opens on 25 July