During early development in the early 1990s, mainly focused around the screenplay by Sam Hamm, early casting rumors included Robin Williams as Rorschach, Jamie Lee Curtis as Silk Spectre, Gary Busey as the Comedian, and both Richard Gere and Kevin Costner considered for the role of NiteOwl. The project underwent numerous rewrites under director Terry Gilliam and his collaborator Charles McKeown, but got eventually shelved by Warner Bros.
Darren Aronofsky was going to direct the film but dropped out after scheduling conflicts with The Fountain (2006).
In 2004, Paul Greengrass was attached as a director, a script was written and conceptual work had begun when Paramount suddenly decided to put the movie on hold for the time being. A short time after that Greengrass left the project to work on the movie United 93 (2006) instead. After being put into turnaround, the rights were reacquired by Warners in 2006.
The first official image from the director Zack Snyder, a test shot of Rorshach holding The Comedian's button, was actually hidden in the trailer for the film 300 (2006). It features one of the director's associates wearing a makeshift mask in front of a composite New York backdrop, and was created during filming on 300 (2006) as an experiment by Snyder to establish the mood and look of his proposed Watchmen (2009) project. Snyder's wife bet $100 against him that no one would discover it, while Zack was convinced that someone would find it almost immediately. Zack won.
Actor Doug Hutchison had expressed interest in playing the role of Rorschach. An online campaign attracted a great deal of support for this casting choice and approaches were made to the studio by his agents in this regard, resulting in the casting director giving the actor an audition for the role which was put on tape for Snyder's consideration.
Alan Moore, writer of the original comic book was asked to write a script back in the late 1980s, but declined. The studio then enlisted in the aid of Sam Hamm.
Terry Gilliam considered directing this film as early as 1989, but after several unsatisfactory drafts of the screenplay, decided the material unfilmable as a feature production. Gilliam had said he would consider directing it as a five hour miniseries at least.
Both Tom Cruise and Jude Law expressed interest in the role of Ozymandias.
Simon Pegg met with the producers to discuss the role of Rorschach when Paul Greengrass was attached to direct at Paramount, but nothing was agreed for certain before that project went into turnaround.
Zack Snyder based his storyboards for the film on the panels of the actual graphic novel. He has stated that in order to be true to the source when adapting a graphic novel to the screen, the original visual art should be respected as much as the written portion.
Zack Snyder personally asked Dave Gibbons, the artist who drew the original graphic novel, to design the first teaser poster for the film. Gibbons enthusiastically agreed and designed the poster to have subtle visual clues hinting at the film's plot.
Though author Alan Moore preemptively disowned all filmed adaptations of his work, Zack Snyder has said that his ultimate hope is that someday Moore will actually see the film and feel that it is a decent representation of the original graphic novel.
When asked in an interview with ReelzChannel.com about original 'Watchmen' writer Alan Moore's dismissal of his movie, Snyder was quoted as saying "Worst case scenario - Alan puts the movie on his DVD player on a cold Sunday in London and watches and says, 'Yeah, that doesn't suck too bad.'" When this was brought up with Moore himself in a later interview in the British Tripwire comics fanzine, the writer commented "That's the worst case scenario? I think he's underestimated what the worst case scenario would be... that's never going to happen in my DVD player in 'London' [Moore very famously lives in Northampton]. I'm never going to watch this fucking thing."
The rights to produce this movie were acquired in a deal that originally also included adaptation rights to V for Vendetta (2005), also authored by Alan Moore. "Vendetta"-producer Joel Silver was also going to produce this one when Terry Gilliam was still attached as a director.