Did you ever think that a Watchmen film would get made? People like Terry Gilliam and Paul Greengrass tried and couldn't get it off the ground.
"I always looked upon it as a bit like having a ticket in a lottery. The chances are it won't come up, and if it doesn't come up I won't be disappointed. I haven't been holding my breath all these years thinking, 'Oh, please make a movie of it, it's gotta be a movie'. But the fact that it is being done, and it's being done quite well, I'm quite excited about it."
What did Zack Snyder seek advice about when he started making it?
"He basically wanted me to look at the screenplay to make sure there was nothing in it that particularly offended me. I'm realistic enough to know that things have to be adapted and changed and compressed. I gave him comment on that. I did do some visualisations of scenes that hadn't been in the original graphic novel. I gave advice to the actors on set on how to deliver the lines. They didn't have to do that at all, and I kind of suspect on some of the previous productions they wouldn't have bothered."
Are you happy that the film uses a Cold War backdrop and doesn't update the story to involve the War on Terror?
"Yeah, I think that's the absolute key to it because it makes it classic. It sets it in a historical timeframe and we can compare what's happening nowadays without it trying to be 'what's happening at the moment'. There's always a terrible thing with films that deal with pop culture that if it deals with the pop culture of today it gets really old, really quickly and I don't think that will happen with Watchmen."
Do you think Watchmen can please fans of the original book and people who've never read the comic before?
"I do think so. I thought as a cinematic experience it was unlike anything I'd ever had before. The fact that a lot of the images came out of my head made it an unusual experience for me, but it did have a pace to it, it did have a drive to it. It has got the richness that the comic book's got. I've seen the opening ten minutes of it maybe four or five times and I'm still catching details and nuances in it that I didn't see to begin with. I think the fans are going to love that. I think the general movie-going population, they're now familiar enough with superhero movies that they know what we're on about. They know the things that are being deconstructed."
How do you think people will take to Rorschach? He's the protagonist, but he's psychotic.
"I can almost imagine him entering into the language with people saying 'Don't do a Rorschach on me, man'. He's very elemental, a very novel character. Just as all the characters are archetypal - there's the Batman equivalent, the feisty female heroine, the Superman - Rorschach is like the gumshoe detective or the masked vigilante taken way out of everyone's comfort zone. The ultimate vigilante where everything is black and white. I put him in the same kind of bag as Hitler and Margaret Thatcher - you might not like them but you can't deny that there's something very attractive about someone who has no grey areas."
Song lyrics are quoted throughout the book, will we hear those Bob Dylan and Elvis Costello tracks in the film?
"Those songs are in the film. Quite a lot of the inspiration from it comes from the Bob Dylan song 'Desolation Row', which has got the line 'At midnight all the agents and the superhuman crew, come out and round up everyone that knows more than they do', which is what happens in the first issue. The title montage is accompanied by Dylan's 'The Times They Are a-Changin'. 'All Along The Watchtower' is in there. There's a couple of surprises, one of them I was unsure about initially, but it fits perfectly. It's a real pop-cultural mash-up."
Can you understand why writer Alan Moore has taken his name off the movie?
"Absolutely. He has had some bad experiences with Hollywood and he doesn't want to repeat them. He doesn't take the moral high-ground, he's got no problem with me doing it. He's indifferent to the whole thing. He doesn't want to talk about it, doesn't want to know anything about it. I regret that because that comes out of a certain degree of unhappiness on his part."
Are any of your other comics getting interest from Hollywood?
"There's been nothing picked up. There was a series I did with Frank Miller called Martha Washington, which in fact is longer than Watchmen, it's about 500 pages. Frank's enjoying a certain amount of success in Hollywood and I wouldn't be surprised if something happens with that. I think that would make a great movie. People misunderstand Frank, they think he's very grim and right-wing, but he's got his tongue very firmly in his cheek. Martha Washington is a war story but it's quite satirical and I think has a strange resonance with what's happening in the world today."
Watchmen is released in cinemas on March 6.