Director Zack Snyder and his wife producer Deborah Snyder stepped down from finishing the film, after the suicide of Zack Snyder's daughter in March 2017. They tried to remain on the film as a way to work through the difficulty, but decided after two months to step away from the project to spend time with their family. Joss Whedon, who had signed on for Batgirl, took over as director, managing additional scenes that need to be included in the final cut. Warner Brothers have stated that Joss will direct and write in the same style as Zack so there won't be any tonal shifts or obvious changes in style. However, Joss Whedon controversially fired Zack Snyder's composer Junkie XL, and replaced him with Danny Elfman.
Extensive reshoots in London and Los Angeles in mid-2017 added a cost of approximately $25 million to the film's budget. Henry Cavill worked on the reshoots and M:I 6 - Mission Impossible (2018) at the same time. He had to sport a mustache for his role in the latter project, however Paramount refused to let the actor shave it off for the time he played Superman again. This meant that Cavill's facial hair had to be digitally removed in post-production.
One of the Gotham scenes during the prologue has a building with "Janus" written on it. This refers to Janus Cosmetics, run by Batman's enemy the crime boss Black Mask. Black Mask is set to appear in Gotham City Sirens.
Ciarán Hinds portrays Steppenwolf in motion-capture. Hinds was unfamiliar with using the technology and got advice from his friend Liam Neeson, who had earlier done motion-capture acting in A Monster Calls (2016).
Two scenes show Flash and Superman moving quickly neck and neck which is a nod to the classic argument of which hero is faster. However, in Flash Rebirth #3, a resurrected Barry Allen and Superman do a foot race. While Superman is able to stay alongside Flash and even brags about beating him in previous races, Flash finally admits those races were for charity and blasts past Superman, leaving him with a shocked look.
Zack Snyder stated that Justice League was always going to be totally different than Batman v Superman. During the time Warner Bros. invited journalists and bloggers to visit the set, Zack Snyder also stated it was going to have a shorter runtime too.
Billy Crudup plays Barry Allen's (The Flash) father Henry in this film. However, before appearing in the DC Universe, Crudup initially auditioned for and was a top contender for the role of Bruce Wayne/Batman in Batman Begins (2005) before Christian Bale was cast. Crudup also portrayed a DC Comics superhero in the film, "Watchmen."
This movie was initially going to be split into two parts: Justice League Part One and Justice League Part Two, with an alleged singular continuing story line. But by the time filming the idea of the film being in two parts seemed to have quietly gone away, and it is now rumored to be two self-contained movies with two related but separate plots.
The line-up in this film is based on the founding members from the New 52 origin story (with the exception of Green Lantern). During the Silver Age origin story, Martian Manhunter was one of the founding members. He was replaced with Cyborg (who was previously known as a founding member of the New Teen Titans) in the New 52 version.
Holt McCallany, who plays the burglar in the first scene with Batman, said the scene was written and shot by Joss Whedon as comedic, but Warner Bros. preferred to open the film with a more serious tone, and the scene was re-edited. When McCallany returned home to New York, he found a bottle of his favorite champagne at his door and a note from Whedon that said, 'To battles lost. Gratefully, Joss.' McCallany appreciated Whedon's gesture and had the letter framed.
When the film got shown in Iceland (which uses subtitles rather than dub for films with non-Icelandic languages), Jason Momoa's pronunciation of his single line of Icelandic was deemed so unintelligible that it had to be subtitled into Icelandic (often resulting in a big laugh by the audience).
As an April Fool's Day joke, production said Zack Snyder had left the project and that George Miller would be taken up the directing duties. The feedback was quite positive. However, when Joss Whedon replaced Snyder due to the death of Snyder's daughter, feedback was sincerely sympathetic.
In one scene, Alfred (Jeremy Irons) says to Bruce Wayne (Ben Affleck), "One misses the days when one's biggest concerns were exploding wind-up penguins." This is a reference to Batman Returns (1992), where Batman (Michael Keaton) goes up against Catwoman (Michelle Pfeiffer) and the Penguin (Danny DeVito) who had an army of penguins wearing exploding rockets with a plot to destroy Gotham City. The composer of Justice League, Danny Elfman, also composed the original Batman (1989) & Batman Returns (1992) musical scores and he utilizes parts of them in this film.
This was Zack Snyder's first film shot in the 1.85:1 aspect ratio. This was chosen because Snyder had a great experience with filming the IMAX sections of Batman v Superman: Dawn of Justice (2016) and he "sort of fell in love with [the] giant, less rectangular aspect ratio" of 1.85:1 as opposed to the 2.39:1 aspect ratio used in his previous films.
This film will be released on the 25th anniversary of The Death of Superman comic, which was released November 17, 1992; and the 16th anniversary of Justice League (2001) which premiered its first episode November 17, 2001.
Billy Crudup also starred in Watchmen (2009), based on the DC Comics graphic novel of the same name. Crudup portrays Dr. Manhattan, the most powerful being in existence. Watchmen was also directed by Zack Snyder and while the story took place in a parallel universe to the main DC universe, it appears the current DC comic book Rebirth line of comics combined the Watchmen universe with the current DC main universe.
Danny Elfman confirmed that he would be using the Batman theme music from Batman (1989) in the film, and would also use briefly John Williams' Superman theme during "a dark, twisted moment" in the film. Gary Clark Jr. and The White Stripes have also been featured in the Justice League album.
The scene in which Barry Allen/The Flash is grumbling that Bruce Wayne/Batman is sitting in his second favorite chair is an inside joke about "Sheldon's Spot" from The Big Bang Theory (2007). Sheldon is a big fan of The Flash and The Flash also wears t-shirts with Sheldon's quotes in TV series The Flash (2014).
In January 2008, Warner Bros. announced the film was on indefinite hold, allowing options to lapse for the cast. The studio felt the script needed perfecting, which was impossible because of the 2007-2008 Writers Guild of America strike.
Joe Morton who plays Silas Stone in this film and the father/ creator of Cyborg, also starred in Terminator 2 (1991). In both movies he uses futuristic technology that in turn lead to the creation of cyborgs with metal parts and red eyes: the Terminators themselves in Judgement Day, and Cyborg his son in Justice League.
Back in 2007, Jason Reitman was the original choice to direct the film, but he turned it down, as he considered himself an independent filmmaker and preferred to stay out of big budget superhero films.
When the three DC main heroes (Wonder Woman, Batman, Superman) make their first public appearance in the film, a part of their theme music from their respective films (Batman v Superman: Dawn of Justice (2016), Batman (1989), and Superman (1978) - all their cinematic debut films) plays.
Henry Cavill's Superman hairstyle got changed from the previous movies. In this movie Henry parts his hair on the left, which is supposedly perceived as masculine and assertive. In his previous movies both Kal-El, Clark Kent had right partitions which was quite opposite of the comic book version.
The members of the Trinity (Superman, Batman, and Wonder Woman) have appeared in 2 movies each before Justice League. Apart from Batman v Superman: Dawn of Justice (2016) which had them together in a live action movie for the first time, Superman was in Man of Steel (2013), Wonder Woman in Wonder Woman (2017), and Batman in Suicide Squad (2016) (cameo).
Ciarán Hinds is the third actor from the Harry Potter franchise to join the DCEU, following David Thewlis (Ares) and Ezra Miller (Barry Allen/Flash). Gary Oldman was another actor to have starred in a DC, as Jim Gordon in the Dark Knight trilogy, but the movies were set in a different universe.
Joe Morton portrays Silas Stone, a character that shares one striking similarity with Miles Dyson, Morton's character from Terminator 2 (1991). In Terminator 2, Dyson is to blame for Judgement Day based on his influence in Terminator development. In Justice League (2017), Stone is responsible for recreating his son into a cybernetic organism. Both of Morton's characters created pivotal androids, it just happened 26 years apart.
When Arthur Curry (Aquaman) is facing the oncoming ocean wave as he stands at the end of the pier, the bottom of the shot shows the outline of his boots jutting out from his legs. The appearance suggests a tribute to the comic book Aquaman who has fins on his costume that jut out from his calves.
At the end of the film Superman and The Flash have a race to decide who is faster. This is a direct reference to numerous races in the comics like Superman No. 199 and others where both of them have had occasional races to decide who is the fastest man alive. However in the comics, Superman restricts himself to running as opposed to flying, which is a much more strenuous form of locomotion for him and has allowed the much more practiced Flash (In this case, the Wally West version) to win at least once. However, a much later story had Flash (Barry Allen), racing to an emergency with Superman, commenting that those races were for charity and instantly pulls far ahead as he starts running seriously.
After the credits, there is a scene where Lex Luthor is asked to turn around. When he does, it is not him. Deathstroke arrives at a yacht having been invited by Lex Luthor. Deathstroke tells Lex that he better not be wasting his time to which Lex replies "Shouldn't we create a League of our own?" hinting at the creation of The Legion of Doom or Injustice League.
An episode of Rick and Morty (2013) can be seen playing in the background behind Bruce Wayne in Barry Allen's place. The scene shows Rick & Summer defeating the Devil, which mirrors the actions of the League in this film, as Steppenwolf is an allegory for Lucifer.
Henry Cavill started working out for this film on February 5, 2016 and announced it on social media by posting a shirtless picture of his physique, Stating he was setting that physique as a "minimum goal" for his third go-round with the character.
The filmmakers deliberately had the story leave out Superman for the most part: "It's hard to have a Justice League without Superman. But his sacrifice is, in a weird sort of way, the why of the Justice League. So what do you do now with him? What does the team think? What does the world need? All that comes into play."
Victor Stone became Cyborg after suffering near-fatal injuries in an explosion. In the comics Stone got his injuries from a lab accident by a creature from another dimension. The same incident caused also the death of his mother. In the comics, Silas Stone "rebuilds" Victor's body with artificial limbs and organs, not an alien artifact.
When Aquaman heads back to Atlantis at the end of the film, he swims past a humpback whale and her child. This is a reference to the Man of Steel scene in which two similar creatures swim past a floating superman, reminding him of the calming advice his mother gave him when he was a child.