In October 2007, George Miller had cast the Justice League completely, with D.J. Cotrona as Superman, Armie Hammer as Batman, model Megan Gale as Wonder Woman, rapper Common as Green Lantern/John Stewart, Adam Brody as the Flash/Barry Allen, Santiago Cabrera as Aquaman/Arthur Curry, Hugh Keays-Byrne as the Martian Manhunter (J'onn J'onzz) Tereasa Palmer as Talia al Ghul, and Jay Baruchel as Maxwell Lord. However, the film was shelved during production.

This film is being released on the same day the animated series Justice League (2001) first aired sixteen years earlier.

In the trailer, an episode of Rick and Morty (2013) can be seen playing in the background behind Bruce Wayne in Barry Allen's place.

This movie is confirmed to bring together Batman, Superman, Wonder Woman, Aquaman, the Flash, and Cyborg. Mera is confirmed to show up in the film, yet it is unknown whether or not she will be on the team.

Ben Affleck was considered to direct this film.

When Gal Gadot was asked by a reporter about how she would get Wonder Woman's breasts from the comics, she answered, "Wonder Woman is Amazonian, and historically accurate Amazonian women actually had only one breast. So, if I'd really go 'by the book,' it'd be problematic." Gadot practiced Kung Fu, kick boxing, sword fight, jiu jitsu and capoeira as part of her physical preparation for the role.

This film took one decade to come to fruition. A Justice League film entitled "Mortal" was scheduled to be released in 2007, but it got shelved.

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 Bothers 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.

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.

This film marked the second time J.K. Simmons and Willem Dafoe appeared in the same comic book franchise, after Sam Raimi's Spider-Man trilogy (2002-2007).

Chris Terrio finished writing the screenplay as of July 2015.

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).

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.

Laurence Fishburne was asked to reprise his role as Perry White for a cameo, but scheduling conflicts with other projects made him unavailable on the day filming was supposed to take place.

Pre-production of this film started in January 2016.

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.

In September 2007, George Miller had signed on to direct, but by 2010, he finally left the project.

Joss Whedon took over for Zack Snyder, as Snyder left the project for reasons pertaining to his family. Whedon's changes included replacing Junkie XL with Danny Elfman as composer. Whedon and Elfman previously collaborated on Avengers: Age of Ultron (2015).

At one point, Warner Bros. considered making this film in motion-capture animation.

Extensive reshoots in London and Los Angeless 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 will had to be digitally removed in post-production.

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.

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.

Danny Elfman took over from Junkie XL who originally replaced Hans Zimmer who announced his retirement from the "superhero business" and left to work on Tomb Raider (2018).

Marit Allen was originally hired as costume designer, but she died in November 2007.

This is the third live-action appearance of the Justice League after the failed TV pilot Justice League of America (1997) and Smallville (2001).

This is Danny Elfman's eighth superhero franchise, after working on Tim Burton's Batman films, Barry Sonnenfeld's "Men in Black" films, Sam Raimi's Spider-Man films, Hulk (2003), Wanted (2008), Hellboy II: The Golden Army (2008) and Avengers: Age of Ultron (2015).

The first official footage for this film was shown at San Diego Comic Con on July 23, 2016.

The film cast includes three Oscar winners: Ben Affleck, Jeremy Irons, J.K. Simmons; and four Oscar nominees: Amy Adams, Willem Dafoe, Diane Lane and Jesse Eisenberg.

This film will be released on the 25th anniversary of The Death of Superman comic, when it was released November 17, 1992 and as well as the 16th anniversary of Justice League (2001) which premiered it's first episode back in November 17, 2001

Ben Affleck and J.K. Simmons previously appeared together in the films Extract (2009) and The Accountant (2016).

Zack Synder cites Seven Samurai (1954) as an influence on the film.

Danny Elfman used a bit of John Williams's Superman score in the film for a Superman scene.

Lana Wachowski and Lilly Wachowski were, at one point, considered to direct this film.

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.

Kristofer Hivju was rumored to appear as an Ancient Atlantean King.

Wonder Woman stands atop a statue of the Greek goddess Themis, or Justitia to the Romans, better known in modern society as Lady Justice.

Both Jesse Eisenberg and Kiersey Clemons were set to appear as Lex Luthor and Iris West but their scenes were cut.

Jason Momoa and Ciarán Hinds appeared in Game of Thrones (2011).

Willem Dafoe and Diane Lane previously appeared in Streets of Fire (1984).

Ben Affleck and Ciarán Hinds appeared in The Sum of All Fears (2002).

The line-up in this film is based around 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 who was replaced with Cyborg in the New 52 version (who previously was known as one of the founding members for the Teen Titans).

Willem Dafoe previously appeared in American Psycho (2000), opposite former Batman Christian Bale and current Joker Jared Leto.

In Addition to Danny Elfman bringing back the original 1978 Superman score/theme, It's been heavily rumored (due to an interview where this was hinted at) that Elfman will also bring back the score/theme for Afflecks scene(s) as The Batman from the 1989 film Batman. It's unknown whether or not Matt Reeves plans to continue to use the famous Batman 1989 theme/score for his upcoming "film noir" style The Batman Trilogy.

As seen in many clips from the recent Justice League trailers, many of the scenes show the sky being illuminated in a Red hue. This is interesting seeing as a Red Sky is a sign of a post "Flashpoint" timeline in many of the aftermath stories in the comics. This includes post-Flashpoint Paradox comics like Batman, Superman, Wonder Woman, Justice League, where a butterfly-like effect occurs changing the past creating an alternate 'present' & this of course includes The Flash comics. A "Flashpoint" storyline has been announced as the movie for "The Flash" by DC/Warner Bros. - taking place of what was originally planned to be a semi-traditional origin story for Barry Allen becoming "The Flash." Ezra Miller is set to star as well as appearances by Cyborg, Henry Allen, & Iris West. The actors appear to be the same as set up in the previous Snyderverse films.

The second time Ezra Miller and Billy Crudup have worked together. The first was The Stanford Prison Experiment (2015).

This is the third comic-book film saga for Ciarán Hinds, after Road to Perdition (2002) and Ghost Rider: Spirit of Vengeance (2011).

At the Kent farm, Clark is dressed in a red checked suit. This was his outfit from Smallville (2001).

Michael McElhatton and Ciarán Hinds have both starred in Game of Thrones (2011) and films about the King Arthur legend: Ciaran Hinds in Excalibur (1981) and Michael McElhatton in King Arthur: Legend of the Sword (2017).

Ezra Miller is the youngest cast member of this film.

Ben Affleck and Willem Dafoe have both appeared in the Jack Ryan film series. Dafoe was in Clear and Present Danger (1994) while Affleck was in The Sum of All Fears (2002).

Ben Affleck's third time playing Batman/Bruce Wayne (following Batman v Superman: Dawn of Justice (2016) and Suicide Squad (2016)).

After The Flash (Ezra Miller) cameos in Batman v Superman: Dawn of Justice (2016), he warns Bruce Wayne, "You were right about him," and, "Lois is the key to everything," leading to speculation that a rogue Superman may be the main threat in the Justice League: Part One, as well as an introduction to Darkseid.

Zack Snyder 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."

Green Lantern will appear in a post credit scene.

Zack Snyder stated that the film will be inspired by Jack Kirby's "New Gods" comic series (1971-1984). This series saw the introduction of the space tyrant Darkseid.

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 for Batman v Superman: Dawn of Justice (2016), saying that he was setting that physique as a "minimum goal" for his third go-around with the character.

4chan Users leaked that Green Lantern will appear at the end of the film. In the comics Green Lantern (Hal Jordan) was a founding member of the League, but will not be a main part of the film as the previous attempt of adapting Green Lantern to the big screen with Green Lantern (2011) ended in disaster. Instead Green Lantern's first main appearance will be in the announced Green Lantern Corps (2020)

The film is rumored to have more than one villain Steppenwolf has been confirmed but there is a rumor that the film will also have a rogue Superman and an introduction to Darkseid.

Justice League is filming in the UK. And Joe Manganiello hopped on over to the UK recently. He was previously heavily rumored to be in talks for the role of Deathstroke. Manganiello just started following Zack Snyder and David Ayer on Twitter.

After a few years of speculation, it appears that Steppenwolf seems to be (one of) the main villain(s) of the film. Steppenwolf will be working with/for Darkseid who is planned to be a future main villain for either Man Of Steel 2 or a future Justice League sequel. "Darkseid" is considered to be the DC Comics equivalent to Marvels "Thanos." Several fans have pointed out Superman stories from the comics where after he is ressurected - he is under mind control /led to believe & see an alternate present where he believes Lois is dead. This of course makes Superman lose control and become evil with his unlimited power. This story is one of the main plots of "Imjustice: Gods Among Us" video game as well as different various post "Death & Return of Superman" comics. In the comics and the video game - Superman is led to believe The Joker killed Lois, and proceeds to rip Jokers heart out with his bare hands before taking his pain out on the world. This causes the Justice League to try to stop him and find out if Superman can still be saved. It's unclear if either Steppenwolf, Lex Luthor, or Darkseid will be behind the mind control & Superman Ressurection or not.

Superman and the Flash engage in a race to save people. In the comics, the two heroes often competed to see which one was the fastest.