By Kev Geoghegan
Entertainment reporter, BBC News 
Branded “unfilmable”, Watchmen – the cult graphic novel about a group of retired, flawed superheroes – has finally made it to the big screen.
The movie cost around $100m (?70m) and was filmed in Vancouver, CanadaFrom the second the opening credits roll, it is clear Watchmen is not your typical superhero movie.
An ageing vigilante, The Comedian, is attacked in his high-rise apartment before being hurled 10 storeys to his death… in graphic slow motion.
What follows is a two-and-three-quarter hour epic that centres on an outlawed group of deeply flawed former heroes as a Cold War Doomsday clock inches ever closer to midnight and nuclear apocalypse.
First published in 12 parts by DC Comics in 1986, Watchmen was written by the British team of Alan Moore and illustrator Dave Gibbons.
Deconstructing the myth of the superhero, it posed fairly grandiose questions. What if costumed vigilantes really existed?
What kind of person hides behind a mask and takes it upon himself to fight crime? And ultimately, how far would they go to protect humanity?
Numerous attempts to film the book, included by Time magazine in its list of the Top 100 books of the 20th Century, failed to get off the ground.
Respected directors like Terry Gilliam, Paul Greengrass and Darren Aronofsky were all involved at various stages.
And legal wranglings between rival film studios over the adaptation rights threatened to wreck the project altogether.
So it has fallen to Zack Snyder, the man who helmed 2007’s surprise hit 300, to succeed where others have failed.
Action figures
In bringing the novel to the big screen as an 18-certificate movie, Snyder has forgone a sizeable teenage audience by featuring graphic scenes of violence, rape and erectile dysfunction.
“When the script came to me it was a PG-13 movie – two hours long, updated to the war on terror and sequel-able,” said the 43-year-old director.
“The idea that a happy meal could be made out of Watchmen is reason enough not let a kid go and see the movie.”
And yet the merchandising wheel keeps turning, with action figures, costumes, playing cards and lunchboxes already on the market.
This perhaps explains why Moore disassociated himself from the movie, as he has done with every film adapted from his novels.
And there have been several : From Hell starring Johnny Depp, V for Vendetta and the universally panned League of Extraordinary Gentlemen.
“When I first got on the project, he had already divorced himself from it,” said Snyder.
“I remember saying to the producers, ‘When do we go and see Alan?’ They said, ‘It’s not going to happen. He’s asked that we don’t contact him about it.’
“Because I was such a big fan, I thought if that’s what he wants, then that’s what we have to do.”
Building Manhattan
Set in an alternative 1985, with Richard Nixon still in power for a fifth term and the US and Soviet Union at each other’s throats, Watchmen plays out like a murder mystery.
At its centre is Rorschach, a paranoid vigilante whose face is covered with an ink blot mask, who takes it upon himself to investigate The Comedian’s murder. 
Dr Manhattan (right) was created using computer-generated imagery
With the presence of Dr Manhattan – a super being who works for the US Government – straining international tensions further, Rorschach stumbles on a plan that threatens billions of lives.
Billy Crudup plays the blue-skinned Manhattan, the fantastic result of an experiment gone wrong and the only character with genuine superpowers.
The actor was recreated as a computer-generated image and appears as a hugely muscular, frequently naked presence.
“None of it is me,” he revealed. “They used high-resolution photography and laser scanning and built an exact replica of my face and head in a computer.
“Then they drew up that terrific body and put him into action as I watched from afar.”
A Brit abroad
British actor Matthew Goode went straight from making Brideshead Revisited to playing Adrian Veidt, aka Ozymandias, a former Watchman with a dark secret.
“I seem to remember the fans being extremely distressed that I’d been cast,” he told the BBC News website.
“My brother phoned me on the first day of filming and said, ‘I’ve just been on the internet and apparently your casting is by far the least favourable.
“‘They’re very worried you’re going to ruin the entire movie.’ I was like, ‘Thanks boss, I’ll see you in six months. Don’t call ’cause I don’t like you very much any more.'”
Elsewhere Jeffrey Dean Morgan plays The Comedian, a nihilistic, violent and cigar-chomping misogynist.
The character is killed off at the beginning of the film but is subsequently seen in flashbacks.
With shoulder pads decorated with stars and stripes, he is the dark opposite of comic book icon Captain America.
“The Comedian, in one respect, is America’s hero,” said the Grey’s Anatomy regular. “But on the other hand, he’s also America’s dirty little secret.”
With Watchmen released across the UK this weekend, that secret is now definitely out.