Watchmen, once considered unfilmable, was published in 1986 and has gone through several unsuccessful adaptations. The cast of the new version gathered in London for the world premiere.
Malin Ackerman and Carla Gugino play daughter and mother in the film, despite being separated in real life by just seven years.
British actor Matthew Goode started filming his role as Ozymandias after starring in Brideshead Revisited.
Billy Crudup was filmed in a body suit before artists created his blue-skinned naked superbeing Dr Manhattan.
The traditional red carpet was replaced by the yellow of the novel's smiley-faced symbol in London's Leicester Square.
Jeffrey Dean Morgan, who plays cigar-chomping anti-hero The Comedian, won a legion of female fans for his role in Grey's Anatomy.
Former child actor and 2007 Oscar nominee Jackie Earle Haley plays the mysterious masked vigilante Rorschach.
Guests at the premiere included Jonathan Ross, pictured with his wife Jane.