"We just wanted to give it a sense of fun, of Rock 'N' Roll,"says director Jon Favreau of ambitious Marvel Studios blockbuster Iron Man. "It's gotta have a lot of attitude." With Hollywood bad boy Robert Downey Jr. donning the red-and gold power-suit, there's a very good chance it will....

We've got a question for you, and we want an honest answer. Who's the last movie star you'd expect to see on the cover of Empire headlining a major summer blockbuster tentpole event movie. It's got to be Robert Downey Jr., right?

Not because of a lack of talent, of course. Downey Jr. is a wonderful, electric, natural talent, with an Oscar nomination to his name, and has been for many years. No it's because of the drugs. And the rehab. And the arrests. He's been ploughing the comeback trail for a while now, and is making great progress. But when it comes to toplining an event movie, nobody would go near him with the proverbial tentpole. And yet there he is, on our cover, sporting a fine goatee as billionaire playboy and genius weapons designer Tony Stark, the alter-ego of the invincible Iron Man, the latest Marvel superhero to make a splash on the big screen. If you were honest enough to say 'yes' to our question, don't be ashamed. Downey Jr. himself is still mildly surprised to find that he bagged this particular gig.

"I'd never had an opportunity to do something like this, that I thought could be so good and could be with the right people," he says, taking "$1,170 of ADR time" out of his post-production schedule to talk with Empire. "And I felt like I might not get a shot at doing it because of the wreckage of my past, even though it had been long enough, in my eyes."

But it's good to see things haven't gone to his head. "I'm used to being in control now I'm Tony Stark," he laughs. "You're fired. No - I'll put out a hit on you ..."

"There are so many superhero movies now, how do you differentiate yourself?" asks director Jon Favreau, sporting a black Iron Man T-shirt with glow-in-the-dark logo and a semi-shaved head for his role as a cage fighter in the new Vince Vaughn comedy, Four Christmases. "What makes you a unique property that has something to say?" And if we can continue the honesty theme, admit it, you're thinking the same thing yourself. After all, this summer alone sees Hellboy.

The Incredible Hulk and Batman return for second (well, in Batman's case, sixth) silver-screen helpings, while Will Smith's Hancock (not based on a comic, incidentally) and our boy in the shiny suit are the nervous debutantes. That's a lot of ker-pow for your buck, and it could be all too easy to get lost in the rush. Iron Man has a clear advantage - it's first out of the traps. But as Jimmy Cricket was fond of saying, "C'mere, there's more."

Looking around Favreau's office, you instantly see that Iron Man's appearance sets him apart from Batman's gloom. A shelf heaving with Iron Man toys and memorabilia stands near the door, including a sign with Favreau's watchword for the movie: "Plausibility." On a cabinet behind his desk sits a Sideshow Collectibles statuette of the iconic Iron Man pose by superstar Adi Granov, which formed the template for the ILM cover on our September '07 issue, while the coffee table is currently playing host to a number of framed sketches by Granov, specially drawn for his new chum, Favreau.

Into the next room and we enter concept art heaven. This includes several striking shots of Stark testing various versions of the Iron Man armour, which he's forced to build after being taken hostage in Afghanistan while on a promotional recce. Being a genius, though, Stark turns the tables on his captors and constructs a bulky metal suit complete with an array of weapons, as weIl as a chestplate that keeps him alive by preventing a piece of shrapnel that's buried in his chest from piercing his heart. Using the suit to bust out, he returns to America, refines it and becomes Iron Man, champion of truth, justice... all that stuff.

The concept art takes us through early versions of the MK I armour (bigger, uglier, held together by sticky-back plastic) through to what Favreau calls the "Howard Hughes prototype" MK II, and finally the beautiful sleek, gold-and-red MK III, with its repulsor beams, supersonic flight and extraordinary strength. It's the MK III which features in several mouth-watering sketches, showing 0l' Shellhead facing off against the movie's biggest villain Jeff Bridges' Iron Monger, a bigger, stronger and more advanced version of Stark's arrnour.

"One of the big things that I really had a vision for from the beginning," says Favreau, noting Empire's admiring glance, "was that you needed to have some sort of confrontation between Tony and someone in another overwhelming armoured suit. He has to face the next gen, in a RoboCop kind of way, of his suit." All weIl and good, but to stand out from the crowd, you have to have something a little extra on your side.

There's a political aspect to Iron Man, but ultimately it's the tone, it's the humour, it's the storytelling," explains Favreau. Really though, it's about Robert Downey Jr., whose very presence convinced Gwyneth Paltrow to sign on as Pepper Potts, Stark's secretary-love interest, and whose offbeat, charming presence indicates that Iron Man isn't just your average comic-book flick.

"When we first started talking about the movie, here was a hero with demons," says Favreau. "He's struggling, and there's a seriousness to him and a heaviness. Now it's Robert's movie - it's more fun and exciting than it is heavy. Ours has turned into the kinder, gentler superhero movie by comparison to what else is out there. We just wanted to give it a sense of fun - of rock 'n' roll. It's gotta have a lot of attitude, because that's what Tony Stark has."

Judging from the footage we've seen at Comic-Con, online and in the editing suite, Downey Jr.'s portrayal of Stark could be the kind of leftfield turn that marked out Johnny Depp's Captain Jack Sparrow as one for the ages (and look what that did for his career). This Tony Stark is a volatile, swaggering, arrogant, conflicted, wise-cracking, tortured, flippant brainiac who's been to the dark side and has come back out, blinking, into the light. Not entirely unlike the guy playing him.

"I could relate to it," says 42 year-old Downey Jr. "And, yeah, at a certain point, we were sitting in the Stark private plane set and someone was like, 'What's it like playing Tony Stark?' And I looked at them for a second and thought: 'What are they talking about? I am Tony Stark!' But, God, what a great character - one who's kind of a smart-ass and really not even all that nice a guy for the most part. Then he has this very humanising experience. I guess he's more likeable af ter his awakening and this ordeal he goes through. But it's not like all of a sudden he's like, 'Gotta rescue that cat! I'm trippin' on that rescue-cat!"'

It could all have been so different, of course. Back when the property was being developed at New Line, with David Hayter and then Nick Cassavetes on board as director, Torn Cruise was attached to the role. But nothing coalesced and the rights reverted back to Marvel, which chose Iron Man as its first fully self-funded movie. And suddenly the pressure to fill Stark's shell-suit with a big name diminished.

"Iron Man is the $20 million star of the movie," admits Favreau. "He's the guy that's going to sell the tickets and put asses on the seats."

So a list of possibilities was drawn up. Downey Jr.'s name kept arising as a dark-horse candidate, and a curious Favreau set up a meeting, despite knowing that casting the actor would pretty much be nigh-on impossible.

"He didn't fulfill any of the criteria that I was presented, but I've always loved his work," explains Favreau. "When I met with him, it was just me and him. And Robert was adamant: "This is the part I was meant to play. I am the guy for this role.' And I came back and said: 'This guy looks fantastic, he's enthusiastic and I really think he could be the guy."'

But there was a lot of tossing and turning before Favreau finally got the Stark of his dreams. For a while, it wasn't just 'touch and go'; it was 'no'.

"When it wasn't going to work out, I literally could not sleep at night," laughs Favreau. "And Robert said, 'With your permission, and I understand what you're saying, I'd like to hold out hope here'. He was relentless and patient and did everything he could, and won the race. And now I look like a genius!"

Downey Jr., for his own part, can't really explain why he hung in there. "I just kept going," he says. "I'm not one to usually make great calls before the game starts, but I was pretty certain. It was in the air..."

When Kevin Feige succeeded Avi Arad as big cheese numero ono at Marvel Studios (his real job title is President of Productions) in 2006, the company had secured a deal that allowed it, for the first time, to produce its own films with its own money and without another studio as senior partner - as was the case with Sony's Spider-Man movies, Fox's X-Men series, and every other Marvel movie to date. Iron Man had been earmarked as the first Marvel solo project, and now Feige - an affable geek made good - found himself with one heck of a fust decision to make: Robert Downey Jr. as Tony Stark - yes or no?

"There's a reason why we're doing these films ourselves," says Feige. "Yes, to have a bigger stake in them financially, but also to do this in a different way - one where we can stay more true to the comics. When we looked at our biggest decision on our first film, I didn't want to make a decision that could have been made at another studio. Jon had been losing sleep. I was never losing sleep because I said, 'Okay, I'm in charge now. I have the reins. Let's see if that is the case. If it is, we'll get Robert.' It started out as a potentially risky decision, but now Jon and I were certain that the only risky decision would have been not to hire him."

Risky decisions are what Marvel's all about at the moment. Iron Man and The Incredible Hulk are the first two movies to be produced independently by the studio and, if they're not successful, could well be the only two. Yet that's not stopping Feige and co. being hugely ambitious, with plans for movies stretching to 2012 and beyond.

And it doesn't stop there. Downey Ir. has signed on to play Tony Stark in three Iron Man movies. But if the rumours are to be believed, he'll show up on our screens as Stark long before Iron Man II's OS boots up. In Iune, to be exact, when he will appear briefly in The Incredible Hulk, in the first proper example of a big-screen superhero crossover.

This kind of thing happens all the time in comic books. There you'll be reading the latest issue of X-Men, and suddenly Spider-Man will show up, have a bit of banter or a spot of fisticuffs, and then bugger off again. But it hasn't happened yet on the big screen, despite the fact that Spider-Man, Daredevil and the Fantastic Four all live in New York City (Iron Man is an LA resident, by the way). As far as the movies are concerned, they might as well live on different planets. This, obviously, has a lot to do with the rights belonging to different studios, but Feige is keen to make this a thing of the past.

"I've never been shy about acknowledging that, yes, one of the advantages of having these characters under one roof is that we can potentiany cross-pollinate," says Feige, whose ultimate ambition is an Avengers movie, combining Captain Aroerica, Iron Man, the Hulk, Thor and, erm, Ant-Man. "We now are in a position where perhaps we can begin to suggest that our heroes, as they do in the comics, inhabit the same world, whether that means crossing paths with them, or hearing things. It's a delicate topic and an ongoing creative brainstorm."

So, how does that brainstorm lead to Stark showing up in The Incredible Hulk, as confirmed recently by Hulk co-star William Hurt? Feige laughs, and pauses. "I like rumours very much," he says. "Sometimes they're quite accurate. Sometimes they're off the mark. And I would like them aIl to remain in that speculative realm for the time being."

Frustrated, we turn our attention to Favreau, in the hope of cracking another rumour - that Samuel L. Jackson shows up in Iron Man as Nick Fury, Agent of S. H. I. E. L. D., the Marvel military bureau. But he's equaIly obdurate.

"You keep reaching for that one," he laughs, after a flurry of sneaky questions featuring the words 'Nick' and 'Fury'. "It's a little bit of smoke and mirrors until the movie comes out. We don't want people to know every little thing about the movie so by the time it comes out, they feel they're over it."

At this, Feige walks into the room with a quizzical expression on his face. "I already told him that Thor shows up in Hulk," says Favreau, with mock embarrassment.

"Thanks a lot!" deadpans the producer.

"They fight at the end," adds Favreau.

Feige grimaces. "Now you've spoiled it."

While Feige and Favreau may be keeping their cards close to their chest on the spin-off/crossover front, they're more open when it comes to enfranchisement. In other words, they're not in this to make one Iron Man film. They're in this to make two, or three, or four. You could caIl this crass commercialisation; but it's simple supply-and-demand economics of which Adam Smith ( the father of modern economics) would no doubt approve.

And, as with pretty much all cornic-book movies, there is a sense that - no matter how fun and rock 'n' roll Iron Man may be - it's doing the heavy lifting for the next episode, in which he will really prove his metal mettle.

"The first movie's always hard, because you have to teIl the origin story, and it's so much screentime. But it's also the learning curve of the hero," says Favreau. "He doesn't just climb into the suit - he has to invent each part of it and figure it out. So you really get the sense that by the time he is Iron Man, he has now eamed it. Now you've paid those bills and you've paid them well, and everybody's with you and now you can explore what happens with Iron Man from this point on."

And there's a lot that can happen. It's unlikely that Bridges' Stane/Iron Monger will be back for a second helping, but Iron Man foes waiting in the wings include Russian bad guy Crimson Dynamo (considered for this movie until relatively late in prep), Titanium Man, the hardcore techno-shock of the Extremis virus which reboots the human body to its maximum potential, and Iron Man's Big Bad, Chinese megalomaniac The Mandarin, whose function in the first movie is to act as a shadowy Emperor to Stane's Darth Vader. "We needed the first movie to be able to understand what our tone was, and so the Mandarin looms in the background," explains Favreau.

And then there are the other classic story arcs from Iron Man history - the Demon In A Bottlie storyline, where Stark is crippled by raging alcoholism, and the War Machine saga, where Stark's best friend, Jim Rhodes (played by Terrence Howard), dons the Iron Man armour after Stark quits, and eventually ends up going toe-to-toe with his old pal in a souped-up version of the suit.

"What are the challenges of being Iron Man?" muses Favreau. "What happens with Rhodey, what happens with War Machine, all that stuff? And then of course the pantheon of villains and the larger Mandarin story. And so my mind is starting to go there now - now that I understand what this movie is."

And if Favreau sounds 1ike he's raring to go, Downey Jr. is positive1y chomping at the bit to don Stark's brassy britches again.

"You damn betcha! I want to do 16 of 'em!" he 1aughs. "But it's a strange thing. Even though we're on other stuff now, when the Iron Man Pavlov's bell rings I'll often find myself getting out of the shower, starting the day, and I'll start mulling over which of the 811 plot lines and foes and entrys there are, and where do you want to start this thing, and what's different in the world." He pauses, and grins. "It's quite a psychic fetish for me."

So, next time you see Robert Downey Jr. on the cover of Empire - it'll be, oh, around 2010, maybe 2011 - don't be so surprised. He belongs there now. And that's our honest answer.