Peter Stormare originally auditioned for the role of Balthazar.
It was really Rachel Weisz in the scene where her character flies backwards through the building. This was achieved by suspending her a few meters high by pulling her vertically. The image is turned 90 degrees in the movie, giving the effect that she is actually pulled back horizontally. The shooting was quite painful. The surrounding office was a miniature, not generated on computer, to achieve the scene.
A life-size replica of Rachel Weisz was made and used as the corpse of Angela Dodson's twin sister Isabel who committed a suicide.
Originally, Tarsem Singh was attached to direct with Nicolas Cage to star. However, the director said that "With Cage, I can not make the film I had wanted to". Soon after Singh left the picture, Cage did as well.
In the comic book "Hellblazer" on which the movie is based, the character of John Constantine is from Liverpool. In the movie, the character is from Los Angeles.
Although the movie Constantine is based on the comic book Hellblazer, the movie title was changed because it was too similar to Hellboy (2004). The movies were scheduled to be released within a short space of time between them and it was decided that having such similar titles would hurt the sales of tickets. Therefore Hellblazer was changed to Constantine.
Ravenscar Hospital is named for a mental institution that features in the Hellblazer comic book series. John Constantine spent four years in and out of Ravenscar after he had a nervous breakdown due to a botched exorcism.
Constantine's line in which he says that he doesn't want Angela to be another ghost following him around is a reference to the comics, where he is haunted by the ghosts of friends who have died because of him.
Shia LaBeouf was recommended to producer Akiva Goldsman for the role of Chaz by Will Smith following his impressive performance in I, Robot (2004). The three of them worked in that film, with Smith and Goldsman as producers.
The look of Hell was based on old footage of nuclear tests, specifically the sudden shock wave immediately after the blast that disintegrated anything in its path, hence the crumbling landscape.
When the possessed girl crawls on the ceiling early in the movie she says, "Papatayin natin sila!" This is a Tagalog (Filipino) phrase meaning "We'll kill them all!"
Aside from John Constantine, the only characters to survive the transition from comic to movie are Ellie (a demoness mostly cut from the original theatrical release), Papa Midnite, Chaz Chandler and Gabriel. All of the other characters were invented for the movie.
Rachel Weisz went to the morgue as a part of the research into her character.
The character of Father Hennessy is a mixture of three of Constantine's allies from the comic book. They are Nige Archer who was a psychic, Rick the Vic who was a priest, and Header who was a portly substance abuser. And, like Hennessy, all are killed for being associated with Constantine.
Constantine slits his wrists, starting with his left, and Lucifer reaches out to claim him with his left hand, in keeping with the traditional depiction of the left ("sinister") side being associated with evil.
The tattoo on Constantine's arms is the alchemical symbol of the Red King, which was worn (by him) for protection. It is "the fire triangle with three radiating arrows below represents the 'Perfect Red King,' the Sulfur of the Philosophers."
The "Spear of Destiny" prop is the same one as used in Hellboy (2004).
CAMEO(R.A. Rondell): (the stunt coordinator) as Man in Land Cruiser.
A character named Ellie, who was a demon Constantine dealt with early on, was almost completely cut from the film. Director Francis Lawrence stated that she was left on the cutting room floor because he wanted Constantine to be completely alone when he meets Angela. Ellie was played by Michelle Monaghan. Her scenes can be seen in the deleted scenes section of the DVD. In the theatrical cut, she can be seen briefly in the hospital scene; when Constantine sets off the sprinkler system, she's the one who exclaims, "Holy Water!"
The appearance of John Constantine in the comics was based on the singer 'Sting'.
The character of John Constantine was originally created by Alan Moore, during his run on DC Comics' "Swamp Thing". However, following his negative experience with From Hell (2001) and The League of Extraordinary Gentlemen (2003), Moore decided to reject all money and credit from Hollywood on any adaptations of his work. Thus, he gave all the money he would've gotten to the artist who drew the character with him, and rejected his own "created by" credit from the film.
On the movie's local premiere at Bergen Cinema, Norway, it had 666 visitors.
The cigarettes that Constantine smokes in the movie are not real Chinese made cigarettes. The name means "Yangtse River" and the package was a special design for the film.
Keep watching after the end credits for an extra scene.
In the original script Hennessy was supposed to die of overeating and get thinner the more he eats. The scripted death was inspired by a character in the first issue of Hellblazer who died the same way.
The original script had the opening in Istanbul, Turkey but had to be changed to the present location because of budget restraints.
The "Holy Hand Grenades" were actually Christmas ornaments filled with water.
The original script had hell as a black void with a floor covered with oil.
According to the Director's Commentary on the DVD, the rag that Constantine lights on fire to defeat the flying demons is a piece of Moses' shroud, given to him by Beeman.
According to the Director's Commentary on the DVD, Constantine's brass knuckles are made from gold that was blessed by a bishop during the crusades.
The Nazi flag used to wrap the Spear of Destiny was destroyed after shooting, to prevent it from falling into the hands of Neo-Nazis.
In the lower right-hand corner of Isabel's toe tag, there's the number 616. Whilst some people interpret the Mark of the Beast to be 666, others interpret it to be 616, hence it's appearance on the toe tag.
It is widely believed that the character of John Constantine was changed to an American so that Keanu Reeves could play the role. The truth is the original script retained his nationality but got no response from producers. So the writer changed him to an American and the script quickly gained attention.
The score credit in the film was originally only Brian Tyler, but Klaus Badelt was brought in by producers late in post-production to help enhance the comedic aspects of the film. Tyler and Badelt share a dual credit in composing the score.
On the side walls of Beeman's bowling alley there is a logo of three balls each having a line that juts off from them, looking more like [666] than anything. This can be seen at the beginning of the scene where Beeman discovers the truth to the demons trying to pass over.
Domino Harvey, the late bounty hunter, makes a cameo as Papa Midnight's Bar. She is seated at a table as an angel, with a demon nibbling her ear. Harvey died in June 2005, just months before the film Domino was released, which was about her life and starred 'Kiera Knightley'.
The Spear of Destiny has featured in many DC titles such as The Spectre, but oddly enough has never been prominently featured in the Hellblazer series.
Besides being addicted to smoking cigarettes, Constatine is seen drinking "Ardbeg" - A Scotch single malt, with a powerful smoked flavour.