The concept for Zack Snyder's gargantuan five-movie story began in Man of Steel (2013) with a script by David Goyer and Christopher Nolan, and from there evolved into a sprawling narrative covering many characters. What started as a standalone film began what Zack Snyder often dubs a "mythology" of epic proportions.
However, the plan has been rewritten on a number of occasions, with changes here and there made to tweak the overarching story in different ways both large and small. Whether out of necessity based on circumstances, artistic preference, or studio mandates, the Snyderverse as known today is the result of a dramatic evolution.
Man of Steel 2 to Batman v Superman
Man of Steel was originally conceived as a standalone Superman film. No grand plan was developed when the movie was. So, shortly before the film's release, Snyder and his team discussed ideas for the proceeding film. In a Forbes interview, he explained how the process went.
Destiny was set when they concluded that the references to Batman would lead to a cameo later in the series, which evolved into a full-on crossover with Batman v Superman and its powerful cast, was the logical next step in the story, being the place they were most eager to go to. Anything else would seem like filler. The "Snyderverse" was born then.
Metallo
The character of Wallace Keefe in Batman v Superman, played by Scoot McNairy, was originally intended to be the supervillain Metallo before the story was rewritten. Concept artist Kelton Cram drew up images of McNairy as the villain, including his amputated legs, while artist Rob McKinnon drew his hulking flying mechanized form.
The motivations for the character are still there, preserved in the final movie, as Keefe blames Superman for his life's collapse and the loss of his legs. In early drafts, this hatred would have made him an ideal fit for the iconic Superman villain with a literal heart of Kryptonite.
Batman v Superman: Snow Edition
Various concept art for Batman v Superman shows that, early in production, the film was intended to be set during a snowy backdrop. Depictions of Bruce Wayne’s glass house, the Heroes Park monument, and the fight between Batman and Superman, and more would all have been blanketed in white, similar to Shazam! (2018).
An IMAX camera test with Amy Adams for Clark's funeral was also conducted in the snow. It is interesting to imagine how the film might have been in such a setting, but whether due to inconveniences or an artistic preference befitting the movie's "fall" motif, the movie was set in the Autumn for a wetter, grimier aesthetic.
Enter Chris Terrio
In a bombastic interview with Vanity Fair, writer Chris Terrio explained that the studio wanted the original script for Batman v Superman to be a much darker film with a Batman whose intense violence was glorified. After being brought in by Ben Affleck to replace David Goyer, Terrio set about reworking many elements like this while adding a more prominent political motif.
With Zack Snyder, the duo fought tooth and nail to have their vision of the movie, with the only great lost battle being the title which they found to be misleading given the movie's character-driven narrative over-focusing on the titular battle between Batman and Superman.
Lex Luthor Inspiring the Heroes' Names
In an interview with Empire Podcast (00:13:08), Snyder indicated that Lex Luthor was the unintentional creator of several of these heroes' aliases, as their distinct logos and names would get their start in these files Lex had assembled to document them. Snyder felt it was egotistical for a character like Diana Prince, for example, to call herself "Wonder Woman."
Evidently, this idea was removed from the script for Justice League in the intervening days following this interview before filming on the movie began, as "Aquaman" seems to be named for his mythology, "Wonder Woman" is first used by Barry, and no one refers to Barry as "The Flash."
Additional Humor in Justice League
Following the tumultuous release of Batman v Superman, Warner Bros. found themselves eager to brighten up their DC Extended Cinematic Universe however they could, which emphasized adding additional humor to Justice League with new dialogue by Geoff Johns and persisting into Joss Whedon's cut.
Snyder would later express his satisfaction with being able to remove much of the added comedy for his version of the film, which included the, “I hear you can talk to fish” line from Bruce Wayne in the movie’s early scenes. In an interview with John Doe Movie Reviews, Snyder said, “There's plenty of things that I was like, 'Thank God I can get this out!'"
No Black Suit
Another change to the script by the studio to make their unfolding universe more palatable for general audiences and closer to the formula of the Marvel Cinematic Universe included removing Superman's iconic black suit from the script for Justice League.
As such, Snyder was forced to shoot the film in the blue suit, though he had conducted tests that would allow his team to more easily turn the suit black in post-production, hoping he could get a special director's cut. He got his wish in this year's Zack Snyder’s Justice League, restoring Superman's black suit in all its shining glory.
Deathstroke and Joker in the Knightmare
In the original storyboards, Joker and Deathstroke were totally absent from the dystopian "Knightmare" future seen at the end of Zack Snyder’s Justice League. It was actually Will Smith's Deadshot in their place, fighting by Batman's side in the hope that their endeavor would make a better timeline and save his beloved daughter.
He would have employed Kryptonite bullets in their battle to defeat Superman, who had been brainwashed to serve Darkseid by the Anti-Life Equation. It is clear that, over time, Snyder came to find Deathstroke and Joker more compelling characters to join Batman in his post-apocalyptic quest to change history.
Lois and Bruce Romance
A significant subject of contention regarding the Justice League storyboards was the reveal that, originally, following the death of Superman, a grieving Lois would confide in Bruce Wayne. They would develop a relationship that would result in Lois bearing their son. Resurrecting Superman would be a decision weighing heavily on Bruce for this reason, knowing he could not be with Lois.
Following Batman's heroic sacrifice in Justice League 3, this truth would be revealed to Superman, who would raise Bruce's son as his own. This was found to be a controversial move by those who felt it was disrespectful to Superman. Nevertheless, the concept was removed from the Justice League script and Snyder confirmed in Vanity Fair that Clark would raise his own son.
Menalippe
As revealed in the storyboards for the proceeding Justice League 2 and Justice League 3, Wonder Woman was originally warned of Steppenwolf's invasion by the Amazon Menalippe, who traveled to man's world from Themyscira to deliver the essential warning.
For whatever reason, this character's role was significantly cut down in the final film, and Diana was warned of the coming catastrophe by the nifty Arrow of Artemis dispatched long-distance by divine forces to lead her to uncover the ancient story of Darkseid’s first invasion of Earth.