Two of Peter Maximoff (Quicksilver)'s relations are implied but never outright stated in the film due to copyright issues. He first remarks to Magneto that his mom used to know someone that could manipulate metal - in the comics, Magneto is in fact Quicksilver's father. This is further implied when Peter's Mother sees Magneto on television and reacts with horror and recognition. A deleted scene also addressed that Peter has a sister - Wanda Maximoff, also known as Scarlet Witch.
Patrick Stewart and Ian McKellen were performing in a touring production of "Waiting for Godot" when Bryan Singer approached the actors about reprising their respective roles as Professor X and Magneto. According to McKellen, both men were utterly shocked as they thought they'd passed their roles on to James McAvoy and Michael Fassbender, and would never play the characters again. Both Stewart and McKellen were delighted to return to two of their most popular roles, and to work with the younger actors playing the same characters as well.
The addition of Evan Peters as Pietro Maximoff/Quicksilver to the cast sparked wide discussion over the direction of the character who is also slated to appear in Avengers: Age of Ultron (2015). Quicksilver had been discussed previously as a potential character in both X-Men: The Last Stand (2006) and The Avengers (2012), but legal complexities over the license to the character resulted in his omission from both films. However, in May 2013 both Marvel and Fox Studios announced a resolution to the previous legal issues, and that Quicksilver would appear in this film as well as an Avengers sequel, though under certain parameters: no reference to Quicksilver's membership in the Avengers can be made in an "X-Men" film, and no allusion to his relations to the X-Men or Magneto (the character's father) can be made in an "Avengers" film; the rights agreement between Fox and Marvel even goes so far as to stipulate the character cannot be referred to as a "mutant" in any Marvel film. Additionally, the day after the announcement of Peters's casting, Marvel and Fox entered into a legal standoff over provisions of the rights agreement for the character, including the issue of whether Peters would be allowed to portray Quicksilver in any other film outside the "X-Men" franchise, possibly necessitating a second actor to play Quicksilver in any Marvel film, resulting in two different versions of the same character appearing in two competing film series. Ultimately, Fox and Marvel decided to cast different actors in the part for the "X-Men" and "Avengers" films, with Aaron Taylor-Johnson taking on the role in the latter sequel, thus preventing any connection between the two franchises and keeping the X-Men confined to a separate universe from those of the Marvel cinematic universe.
According to Peter Dinklage, Bryan Singer picked him to play Boliver Trask because of his height: "With my dwarfism, I'm a bit of a mutant. I can't move metal or anything, but I thought of it as self-loathing. Deep down, Trask is quite sensitive about that aspect of himself."
Including his cameo in X-Men: First Class (2011), this will be Hugh Jackman's seventh portrayal of Logan/Wolverine, raising his own record for the most times a comic book character has been played by the same actor in theatrical films. He will also be the only actor to appear in the entire X-Men film series.
The filmmakers selected the "Days of Future Past" storyline because it would allow the filmmakers to reconcile any continuity dissonances within the "X-Men" film series. The time-travel element also allowed actors from the original film series and the intended reboot that was X-Men: First Class (2011) to appear in the same film together.
In the scene where Trask and Nixon discuss the implementation of the Sentinel program, an aide is seen switching off a tape recorder. This is a sly reference to the infamous 18 1/2 minute gap on Nixon's Oval Office tapes, long thought to have been deliberately erased by Nixon or his aides to cover-up politically damaging information. Former Nixon adviser H.R. Haldeman has said the erased conversation contained references to Nixon's involvement in the Kennedy Assassination--another subtle joke in the film, as Kennedy is revealed to have been a mutant.
According to Bryan Singer, he had a two-hour discussion with James Cameron, director of the time-travel films The Terminator (1984) and Terminator 2: Judgment Day (1991), about how to make the time-travel concept feasible and workable within the film. The concepts the two discussed included alternate universes and string theory (a field of quantum physics that define multiple universes).
Bryan Singer filmed Quicksilver's scenes in a special format of 3600 frames per second. This means that Quicksilver will be moving 150 times faster than normal. The camera was used to record close-ups and movements of Evan Peters, as well as the guards he encountered.
The dissertation Bolivar Trask reads from during his senate committee hearing, which outlines that the emergence of Homo Sapien lead to the extinction of the less evolved Neanderthal ancestors, was written by Charles Xavier and was partially read to Mystique in X-Men: First Class (2011).
When Matthew Vaughn was going to direct, he was going to make the film a direct sequel to X-Men: First Class (2011) and have it set in the 1970s. Early ideas included an opening with the Kennedy assassination being caused by Magneto, and mutant encounters set in the Civil rights movement/the Vietnam War. When Singer took over, he integrated these concepts into a viral marketing campaign to set up the action of the film. In this alternate history, Magneto is arrested and imprisoned for the assassination of Kennedy, but maintains his innocence. The "Bent Bullet" Theory (a reference to the real life "Magic Bullet" Theory criticized by conspiracy theorists) holds that the Warren Commission determined that Magneto manipulated Lee Harvey Oswald's bullets to kill the President in retribution for the murder of the mutants Azazel and Tempest (from X-Men: First Class (2011), though in the film Tempest was codenamed Angel) by the CIA. Conspiracy theorists, based on Magneto's testimony, insist however that Magneto had tried to prevent the murder of Kennedy, and that the true shooter was not Oswald, but Mystique in disguise who, with the help of Emma Frost (also from "First Class") framed Magneto, and manipulated Jack Ruby into later murdering Oswald. The theory also posits that Mystique offered to double as Kennedy in an attempt to grab power, all of which backfired horribly, leading to anti-mutant hostilities.
Production designer John Myhre described the future Sentinels as having evolved from machines into biomechanical weapons: "They are almost made up of magnetic plates slapped over one another, imagining that the plates could contract or grow, so the Sentinel can be skinny to get through a small space or the plates can open up to become a bigger shape. They have become virtually unstoppable - the ultimate version that can actually, in principle, stop the X-Men."
The release of the teaser trailer for this film ignited such interest, director Bryan Singer made the unprecedented move of recording an actual commentary track to it the following day, explaining the significance of certain scenes and offering more insight into what to expect from the film.
Jason Flemyng was originally set to reprise his role as Azazel when Matthew Vaughn was still set to direct. When Vaughn left, the storyline was dropped in favor of the time travel/crossover storyline, and Azazel's role cut from the script to accommodate characters from the original "X-Men" film series.
Bryan Singer based Boliver Trask on Adolf Hitler: "As Hitler used the Jews as a scapegoat to bond the darker parts of Europe, he's doing the same thing with mutants. But he wasn't a six foot, perfect blond Aryan - he was a short, funny looking fellow!"
Simon Kinberg said that in the unwritten back story, Bolivar Trask was part of the group responsible for attempting to assassinate the mutant American President JFK. Kinberg also said that Trask had militarian supporters in the US Government and that during the Vietnam War, any soldier with a higher than anticipated kill record would be subjected to tests by Trask Industries to determine whether they were a mutant. Those found to be a mutant were put into quarantine.
Bryan Singer and Peter Dinklage describe Bolivar Trask as a peace-lover: "He feels that humanity will go on fighting each other, unless they can find a common element to unite against; he sees the advent of the mutants as a way to unite people. He sees what he's doing as a good thing - his ambition is definitely blind. He's strove all his life for a certain respect and attention."
During Magneto's fight with the presidential guards, there is a painting behind him. This painting is "Liberty Leading the People", a French painting made to commemorate the 1830 French Revolution, and a symbol of rebellion.
When talking to Beast, Logan says he hopes he isn't a parent. Wolverine has sired a number of children throughout Marvel history: he sired Daken Akihiro (Dark Wolverine), he was cloned to create Laura Kinney (X-23) whom he treats as a daughter, in the "Ultimate Marvel" comics he is the father of Sabertooth and Jimmy Hudson (the second Wolverine) and in the "All-New X-Men" storyline he and Mystique sire Raze Darkholme.
Almost all of the promotional photographs and posters of Major Stryker had the blue enamel of his Combat Infantry Badge "corrected" to green. Blue is the color of the U.S. Army's infantry branch. It appears the right way in the film.
When Hank hacks the surveillance monitors, one of the shows seen on the screen is Star Trek (1966). Patrick Stewart would appear in the Next Generation show as the second Enterprise captain Jean-Luc Picard.
The script called for Logan to wake up in 1973 in boxer shorts. Hugh Jackman vetoed this in favour of waking nude: "In Australia, if you're next to a really good-looking girl, you're not getting out with boxer shorts on or briefs or anything!"
Charles Xavier mentions that he believes Erik curved the bullet used to kill John F. Kennedy. James McAvoy starred in the movie Wanted (2008), itself also based on a comic book. In the movie, McAvoy's character learns he has superhuman abilities inherited from his father (ie genetic abilities, like a mutant power, versus abilities given to him by an outside force), which include the ability to curve bullets to hit a target.
In the film, President John F. Kennedy is heavily implied to be a mutant. In the year previous to this film's release, James Marsden ("Cyclops") portrayed Kennedy and Liev Schreiber (Sabretooth) portrayed his successor Lyndon Johnson in Lee Daniels' The Butler (2013).
According to John Myhre, the past Sentinel robots were inspired by 1970s molded plastics: "It was the idea of being inspired by 70s product design that helps out. We made them a little fun and stylish but also a little retro, and the key is they're not made of metal. That's very important to the story because there's a very powerful mutant."
According to Simon Kinberg, the story's main theme is hope: "It confronts the notions of second chances. It's about characters that are lost trying to find themselves. In the other films, the characters had come into their own and knew who they were. In this one, they're all lost and they're trying to keep it together."
The private jet with tail number N540EA is a Gulfstream IIB, which is a II with the wings of a Gulfstream III. This variant was not FAA approved until 1981. The Gulfstream III from which the wings come was not built until 1979.
Comic book writer-artist John Byrne, who had worked on the "Days of Future Past" comic, was approached for a cameo in the film. He declined stating he disliked the films, and he'd feel "like he was in the Carrie (1976) prom scene".
The trivia items below may give away important plot points.
The cameos of Cyclops (James Marsden) and Jean Grey (Famke Janssen) were so tightly guarded that the actors as well as director Bryan Singer outright lied about their appearance in the movie to keep their return a surprise.
In the post-credits scene, the pan around to the front of the character building the pyramids reveals the silhouette of four individuals on horseback. These are the Four Horsemen of Apocalypse, four super-soldiers he converted and enslaved.
The appearance of the X-Men in the restored future segments resembles their appearance in the X-Men comics almost exactly. There are also hints at changes in relationships, as Rogue and Iceman are seen walking hand in hand, and Kitty and Colossus are seen teaching a class together (implying they're also a couple, as in the comics).
In the "Days of Future Past" comic it was Shadowcat who went back in time; in the film it's Wolverine. According to writer Simon Kinberg, Kitty was intended to be the time-traveller but it didn't work out: "Kitty in the era of young Magneto and Xavier would have been negative 20 years old. The reflex response to that was a character who doesn't age. Wolverine is the only character who would look the same in 1973 as he does in the future." Thus, Wolverine was picked for being an ageless immortal character who would bridge past and future.
Bryan Singer based the time travel in the film on string theory: "Until an object is observed, it hasn't really happened yet. The time-traveller whose consciousness travels through time I call The Observer, and until the Observer returns to where he travelled from, the result hasn't occurred yet. So he can muck about in the past and it isn't until he snaps back that the new future is set. As a result, we have parallel action, and there's underlying tension because there's always that threat Wolverine's consciousness could return to the future and leave the world in an even darker place."
In the "Days of Future Past" comic Mystique tries to assassinate Senator Robert Kelly leading to the genesis of the Sentinel program. In this film Mystique remains the assassin, but as Kelly had appeared in X-Men (2000) her target is now Bolivar Trask (Peter Dinklage).
Originally, there was an action sequence where Rogue (Anna Paquin) is trapped in the X-Mansion (now a Sentinel-run prison facility) and Professor X, Magneto and Iceman rescue her; this sequence was cut as Simon Kinberg and Bryan Singer felt it was taking too much attention away from the main plot and the sequence will appear on the DVD. In the finished film, Rogue is only seen in the "restored" future sequence for a brief moment, though Anna Paquin still gets star billing.
When describing Mystique's capabilities to the President in the Oval Office, Trask tells him that she could take any shape including that of a colonel, a secret service agent, and even the President himself. That is the order of the key shapes she takes on during the film.
According to Simon Kinberg, this film unites ALL the future mutants: "It's this dysfunctional family and these desperate people who are outcasts in their own lives, and they come together, and that's not as emotionally satisfying as an outcast on their own."
The bullet wounds that appear on Wolverine's chest on his arrival to the 1970s is in the form of the Big Dipper. This is a homage to Hokuto no Ken (1984), whose protagonist Kenshiro has the same scar pattern on his chest.
The British movie magazine Empire had a front cover pulled out of production by Bryan Singer as it featured a photograph of Bolivar Trask in a straitjacket; Singer felt it gave the ending of the film away.
The baseball stadium Magneto destroys in the film is the old Robert F. Kennedy (RFK) Memorial stadium. The Washington Senators played there until September 1971 and the Washington Nationals played there in 2005. Since the film takes place in 1973, it makes the stadium employee laying down chalk seem odd since baseball wasn't played there at that time.