The film was originally to be a prequel about Magneto. Screenwriter Sheldon Turner wrote a treatment which he described as "X-Men (2000) meets The Pianist (2002)": the story focused on Magneto's early years as a prisoner of war in a Nazi concentration camp, until liberation by a squad of Allied Forces led by Charles Xavier. They later meet after the war and become friends, and later become rivals. The studio decided to change the film's direction to the early years of the X-Men, but incorporated aspects of Turner's script into the film.
To prepare for his role as Charles Xavier, James McAvoy shaved his head... and learned that the filmmakers wanted Xavier to have a full head of hair in the prequel. Throughout the first month of filming McAvoy had to wear hair extensions.
Although they barely interact during this movie (and in fact are antagonists through most of it), according to the comics canon, Azazel and Mystique eventually have a child together, Kurt Wagner/Nightcrawler (who was played by Alan Cumming in X-Men 2 (2003)).
During the Cerebro sequence, one of the mutants to be seen is Cyclops as a young boy playing with a glove and baseball, noticeable by his sunglasses, and the other being Storm, most noticeable by her haircut.
Caleb Landry Jones auditioned for the film without knowing what X-Men character he was up for, saying he auditioned because it was the film that fit his biotype: "I've got red hair and freckles, I'm not gonna be Batman, Robin or Spider-Man."
When Prof Charles Xavier makes his presentation on human genetic mutation at the CIA HQ, the graphic origin of the X-Men logo can be seen in the left hand image of his final side projection. It is an X-ray crystallography image of the DNA molecule, of the kind created by Dr Rosalind Franklin, which aided Dr Francis Crick and Dr James Watson in discovering the double helix shape of DNA on 28 February 1953, for which they were awarded the 1962 Nobel prize for Physiology or Medicine.
To prepare for his role as Erik Lensherr, Michael Fassbender studied Sir Ian McKellen's performance as Lensherr in the previous X-Films, but also looked through the comics as he decided to make his own version of Magneto: "You want to respect what someone else has done, especially because the fan base really liked what Ian has done with it. But while I could have gone and studied him as a young man and brought that to the performance, I don't think Matthew is very interested in that. So I'm just going my own way and working with whatever is in the comic books and the script."
The set for Xavier's mansion was also used in a TV series called Hex (2004), which also starred Michael Fassbender, who played a character named "Azazeal" which is much like the teleporting mutant named "Azazel".
Matthew Vaughn wanted the film to resemble the productions of the 1960s, with "very traditional framing, and camera movement when it needs to move, not just throwing it around and whizz-bang", and using the anamorphic format "to create a widescreen experience, is emblematic of '60s movies". The director had to hire five cinematographers - with sole credit being given to John Mathieson, who came halfway through the shoot and did half of the film - and four assistant directors to successfully convey the look he wanted for the film.
The uniforms the X-Men wear are colored blue and yellow, in homage to the original blue/yellow suits the X-Men wore in the comics from 1963 (their debut) until (original artist and co-creator) Jack Kirby's departure from the book. After several costume changes throughout the years, the costumes used in X-Men (2000) inspired new black leather uniforms seen in the Grant Morrison written 2001 New X-Men comic).
Matthew Vaughn instructed the cast to do away with all accents in their performances. James McAvoy had planned to copy Patrick Stewart's voice (since McAvoy was going to play a younger version of Stewart's Xavier), but Vaughn quashed it; Vaughn also told Rose Byrne that Moira MacTaggart would not have her trademark Scottish accent in the film (to the Scottish McAvoy's mild disappointment).
In addition to his comic book persona, the character of Sebastian Shaw (Kevin Bacon) takes on qualities of Nazi scientist Josef Mengele. Mengle is noted for his eugenic experimentation and torture often with children, to whom he would offer candy to gain their trust.
During the American/Soviet standoff, the Soviet captain refers to the man behind him as "zampolit", which is inaccurately (but not completely incorrectly) translated in the subtitles as "comrade." A Zampolit is a political officer responsible for political education and enforcing Party loyalty (in this case, on a ship), and is capable of countermanding the orders of the officer he's attached to, if they conflict with Party doctrine. The fact that it's actually the Zampolit that fires the missile to destroy the freighter is a sly bit of irony on the part of the film producers.
According to visual effects supervisor John Dykstra, the biggest problem was with depicting Emma Frost's diamond body "without looking like she was made of Jell-o or the polygon model of a human being". The morphed Frost was rotomated into January Jones in the live-action plates, while still retaining the actress' eyes and lips. As the character kept on going in and out of her diamond form, a motion capture tracking suit could not be employed, so the effects team used a jumpsuit covered in mirrors.
One line was changed in the famous John F. Kennedy speech of Oct 22, 1962. The changed line was voiced by Jim Meskimen. The original line was "It shall be the policy of this nation, to regard any nuclear missile, launched from Cuba against any nation in the western hemisphere, as an attack by the Soviet Union on the United States." In the film the line goes: "..to regard any nuclear missile crossing the embargo line that now surrounds Cuba, as an attack by the Soviet Union..."
Though ostensibly a prequel to the entire "X-Men" film franchise, this movie deliberately ignores continuity points of X-Men: The Last Stand (2006) and X-Men Origins: Wolverine (2009). Matthew Vaughn explained his intention was to "make a good film that could stand on its own two feet regardless of all the other films" and also that could "reboot and start a whole new X-Men franchise". Writer Jane Goldman looked at the film as an "alternate history" for the X-Men - though a reboot, the writers did not want to go fully "against the canon of the X-Men trilogy", citing the various approaches the comic had in over fifty years of publication.
The cities of 1960s Washington and Moscow were created based on photographs of the actual cities; the Russian one in particular had its vehicles and military hardware based on videos of a 1962 Red Square, and a digital army doing an actual Soviet-style march.
The group of mutants gathered by the CIA in this film serve as a catalyst for the formation of the X-Men which consists of Charles Xavier, Erik Lehnsherr (Magneto), Hank McCoy (Beast), Raven Darkholme (Mystique), Alex Summers (Havok), Sean Cassidy (Banshee) and Armando Muñoz (Darwin). In the comics, the original group of X-Men students consisted of Hank McCoy (Beast), Jean Grey, Scott Summers (Cyclops), Bobby Drake (Iceman), and Warren Worthington III (Angel) - all mentored under Professor Charles Xavier (Professor X).
In April 2006 Zak Penn was hired to write and direct this film; he was going to make a prequel about Magneto, in a vein similar to X-Men Origins: Wolverine (2009). However, the filmmakers decided to shift the focus from the early years of one mutant to those of the X-Men. Penn found this approach more interesting than what he'd come up with and so stepped down with his blessing.
Josh Schwartz wrote an early version of the screenplay, but once Bryan Singer became attached, Schwartz's script was ditched as Singer wanted to take the story in a different direction. Jamie Moss was subsequently hired to write a new draft.
Moira MacTaggert uses the call-sign "X-ray Bravo Seven Zero" to identify the X-Men plane. This was the military designation (XB-70) of an experimental nuclear bomber developed in the 1950s, of which two prototypes were built. It was known for its striking, radical design and Mach 3+ speed.
The scene at the water fountain where Moira "hears" Professor X speaking to her while her co-workers have been frozen, was shot during the final sound mix, on the first floor of building 32 on the Twentieth Century Fox lot.
The early version of the X-jet is visually almost identical to the Lockheed SR-71 including the shock diamond effect from the engines. However, the X-jet adds additional engines on the underside for VTOL capability and substantially changes the internal layout from a two person cockpit to a much larger cargo area
The X-Men's plane bears a striking similarity to the Lockheed SR-71, an American supersonic reconnaissance plane. However the original plane was not able to depart vertically or even hover in mid-air. It was used for several high-altitude penetration missions deep inside Soviet territory.
In the original comics of the X-Men; the original characters were Angel, Beast, Marvel Girl (Jean), and Cyclops. Beast, was a strong man with huge feet, who's agility would have matched that of Nightcrawler's.
The trivia items below may give away important plot points.
Hugh Jackman accepted the opportunity to cameo as Logan/Wolverine when he learned he would be the only character in the film to use the word 'fuck'. He improvised the line, "Go fuck yourself," after using 7 other takes to say, "Fuck off". The reaction from McAvoy and Fassbender to the different line was authentic.
With Hugh Jackman's brief cameo as Logan/Wolverine in this film, he is now the first actor to ever play the same comic book superhero in five different movies. And it also makes him the only actor to appear in every single "X-Men" movie.
The ending fight between Charles Xavier and Erik Lensherr was going to have them use their powers, but Matthew Vaughn reasoned that since it was an origin story about the early X-Men the fight had to be a more conventional brawl: "Fox were saying, people want to see super heroes use their powers... but not in this film. Sometimes they just want to punch each other. That, to me, is what's different."