The X-Men movies franchise has been around for more than 15 years, and while the quality of the X-Men movies has had its peaks and valleys, one thing has remained consistent: the X-Men movies continuity is a complete mess. Some fans thought that the time travel of X-Men: Days of Future Past would give 20th Century Fox a chance to set their X-Men movies continuity straight, but instead it's only propagated further continuity confusion. Not all is lost, though. There is still hope in Legion.
Why does the Deadpool from X-Men Origins: Wolverine appear to be in no way related to the Deadpool from Deadpool, despite the fact that they're both played by Ryan Reynolds? How have none of core X-Men characters aged a day between the 1960s of X-Men: First Class and the 1980s of X-Men: Apocalypse, but then suddenly seem to catch up on their aging by the time the original X-Men occurs? How many times has Jubilee flunked her classes if she began attending Xavier's School for Gifted Youngsters in the 1980s of X-Men: Apocalypse, and is still a student in the original X-Men trilogy of the 2000s?
These are the questions that keep X-Men fans up at night, and the X-Men movies continuity seems like it's going to get more even more convoluted as the Deadpool movie, which seems to have one foot in the X-Men movies continuity and one foot in its own world, begets its own sequels, and 20th Century Fox prepares new spinoffs like New Mutants. That's not to mention the upcoming expansion of the X-Men movies franchise into television.
It is somewhat ironic then that possibly the last and best hope for an X-Men movies continuity that makes sense is a television series. The FX series Legion will star Dan Stevens as the mutant David Haller, and David Haller is just the mutant the X-Men movies need to save their continuity.
For those who aren't familiar with relatively obscure characters from X-Men comics, David Haller (created by Chris Claremont and Bill Bill Sienkiewicz in 1985's New Mutants #25) is the son of Professor X and Gabrielle Haller. Haller was a catatonic Holocaust survivor whom Xavier treated with his psychic powers while working at a psychiatric facility in Israel. David possesses immense psionic power that manifests as a number of different abilities, including telekinesis and pyrokinesis. The catch is that his powers manifested after a terrorist attack that fractured his psyche into multiple personalities. Each of those personalities controls a different on of David's abilities, hence the codename "Legion."
The scary part is that on the occasions when Legion has gotten his mind together, he has proven to be one of the most powerful mutants in existence. Legion has rewritten all reality in Marvel Comics on more than one occasion. In the "Legion Quest" story, Legion got it in his head that Professor X would have been a better father if he wasn't always having to deal with that troublemaker Magneto. Legion traveled back in time 20 years to kill Magnus before he could become Magneto, but Xavier sacrificed himself to save his friend. This caused the "Age of Apocalypse" timeline – a world where, without Professor X and his student there to stop him, Apocalypse was able to conquer all of North America – to replace the normal continuity.
While the X-Men were eventually able to undo the "Age of Apocalypse," this wouldn't be the last such incident for Legion. Professor X and Dr. Nemesis would later try to treat his disassociative identity disorder, but Legion's psyche responded by rewriting reality into the "Age of X," a reality where mutants had separated themselves from humanity but were constantly under attack. This reality allowed Legion the opportunity to be the hero he always wanted to be. Later, Legion would finally gain full control of his powers, along with a certain amount peace of mind. As his final act, Legion wrote himself out of existence by rewriting continuity so that he had never been born.
So Legion is a mutant capable of almost casually rewriting continuity, and he's about to be introduced into the X-Men movies universe. This is an opportunity. Legion could be responsible for a full continuity reboot by 20th Century Fox, or he could go on a time travel adventure to do spot fixes on the cracks in X-Men movies continuity. That's an exciting prospect, but Fox probably won't go that route. If Fox wanted a chance to reboot and treat continuity more seriously, they had it with X-Men: Days of Future Past, and I doubt FX will want to mire Legion, its prestige X-Men television series, by allowing it be used as continuity duct tape.
However, that doesn't mean that fans can't do what Fox won't by adopting some head-cannon. Intentionally or unintentionally, every continuity error in the X-Men movies universe could be Legion's fault. We know that Legion is mutant capable of rewriting continuity, that he has trouble controlling his powers, and that he has father issues with Professor X. Take these things into account, and it could explain why Professor X and those around him seem to defy aging, why continuity is so messy, and it could even explain why Professor X so consistently seems to be the center of the X-Men movies universe. It's all because the world of the X-Men movies changes based on Legion's mood, because Legion has been the invisible continuity puppeteer from the start.
This probably isn't the answer that continuity sticklers were looking for and it's probably not a theory that 20th Century Fox would embrace. However, if X-Men fans can allow themselves to place the X-Men movies continuity into Legion's hands, they may just sleep a little better at night.
Legion premieres on FX in 2017.