Priest is directed by Scott Stewart and written by Cory Goodman. The film is based on the Korean comics Priest by Min-Woo Hyung. The project was first announced in March 2005 when the studio Screen Gems bought Goodman's spec script. In January 2006, Andrew Douglas, who directed The Amityville Horror, was attached to direct Priest.In June 2006, actor Gerard Butler entered negotiations to star as the title character, and filming was scheduled to start in Mexico on October 1, 2006. By March 2009, Douglas was replaced by Stewart, who impressed Screen Gems with Legion. Paul Bettany replaced Butler in the starring role. Filming began in August 2009 in Los Angeles, California, and it concluded in November 2009.
Tokyopop flew Min-Woo Hyung to where production was taking place so the comics' creator could visit the art department and discuss the film with Stewart. The film diverges from the comics in following a different timeline of events. The director described Priest's vampires as not being human in origin, and humans bitten by vampires became familiars instead. There are different forms of vampires, such as hive drones, guardians, and a queen. Since the vampires were intended to move quickly, they were fully computer-generated for the film. While vampires are harmed by sunlight in most lore, the film's vampires are instead photosensitive, being albino cave-dwellers. Stewart said, "They are the enemy we don't really understand, but we fought them for centuries. They are mysterious and alien, with their own culture. You sense that they think and communicate, but you don't really understand what they are saying." The director also called Priest an homage to The Searchers with the title character being similar to John Wayne's character and the vampires being similar to the Comanche. Stewart described the priests:
The priests of our story are like Jedi knights. They have these supernatural abilities to fight vampires and they saved humanity before the movie even begins. Now, a generation later, society has moved on from war, and the priests are like pariahs. They're almost like Vietnam vets—they've been cast aside by society and they're now reviled and feared.
Italiano
Alla fine di una guerra secolare tra uomini e vampiri, il mondo conosciuto è completamente scomparso. Al suo posto, macerie e rovine delle vecchie città industriali e, un'ultima roccaforte dell'umanità rappresentata da un Ordine religioso filocristiano, ma evidentemente con altri scopi ben più loschi che l'unione dei popoli ma il controllo del mondo. I superstiti dell'ultima guerra tra umani e vampiri vivono una città costellata da barricate e protezioni, dove la Chiesa ha il controllo di ogni cosa.
Tutto cambia per Ivan Isaacs, quando un branco di vampiri sciolti rapisce sua nipote appena 18enne. Il sacerdote e cacciatore di vampiri, contro gli ordini della sua organizzazione, esce dalla città per dare la caccia ai rapitori della sua familiare, dando vita a un estenuante caccia al vampiro. Ma fuori dalle mura della città non vi è più traccia di passaggio umano, solo un'infinita steppa abitata da vampiri. Ad affiancare Ivan nella sua avventura, anche il fidanzato della nipote, lo sceriffo di un avamposto locale e una sacerdotessa dotata di notevoli abilità nel combattimento.