The X-Men made the transition from comic books to the big screen in 2000 with X-Men. At the time of the film's release, live-action superhero adventures weren't seen as the powerhouses they are today, nor were they taken all that seriously. Nonetheless, the movie was met with critical acclaim, and went on to gross an impressive $296 million worldwide on a $75 million budget. Through its commercial and critical success, the film solidified the X-Men as one of Marvel's most popular superhero teams, and also ushered in a new era of comic book adaptations. Two years after X-Men was released, a sequel, X2, arrived in theaters. The movie proved to be an even bigger success than its predecessor, and Fox quickly built a franchise around Marvel's star team of misunderstood mutant superheroes.

Now, 18 years after X-Men came out, the franchise has expanded a great deal with movies like X-Men: First Class, Logan and Deadpool. Here's the thing, though: with so many years behind it and so many movies functioning under one continuity, the X-Men timeline has become a bit... well, problematic. Throughout the years, fans have noticed numerous inconsistencies in the franchise. Whether it's a character played by two different actors, undefined events, confusing timelines or head-scratching relationship shifts, there have been quite a few continuity mistakes in the span of 11 movies. Given that, we at CBR thought it would be appropriate to take a look back at 20 things about the X-Men timeline that don't make much sense.

20 DEADPOOL'S MODERN EXISTENCE

Wade Wilson made his big screen debut in 2009's X-Men Origins: Wolverine. The film's interpretation of the character received a lot of backlash, and fans were left yearning for a more faithful adaptation of the mercenary. Things turned around for Wilson when his own film hit theaters, and the movie broke away from what came before it, presenting audiences with a comic book-accurate Deadpool.

Some fans attributed Wade Wilson's new iteration to the time-altering events depicted in Days of Future Past. Here's the thing, though -- Deadpool was already an adult in the '70s. Days of Future Past changed things from 1973 onward, meaning that the Deadpool introduced in X-Men Origins: Wolverine should have been completely unaffected by the film's timeline shift.

19 STORM'S AGE

X-Men: First Class features Charles Xavier's first mutant-searching session with Cerebro. As he tries to adapt to the immense power granted to him by the machine, Xavier spots several mutants around the world. One of them happens to be a young version of Storm. The hero's cameo is a nice addition to the movie, but it's also a big problem in the X-Men continuity.

Storm resurfaces in 2016's X-Men: Apocalypse as a teenager who becomes an enforcer for Apocalypse as he tries to take over the world, but according to her brief appearance in First Class, she should already be an adult by the time Apocalypse awakens. Still, who knows? Perhaps there was another white-haired mutant running around in the '60s.

18 CYCLOPS' AGE

During Charles Xavier's aforementioned first session with Cerebro in X-Men: First Class, the mutant spots a young version of Cyclops playing with a ball. The easter egg is exciting, but it becomes extremely confusing when you actually think about it. You see, Cyclops is introduced as a teenager in X-Men: Apocalypse, which is set 21 years after First Class.

That doesn't quite make sense, since going by his fleeting appearance in First Class, Scott should be in his mid to late 20s. Making things even more confusing, X-Men Origins: Wolverine establishes Scott Summers as a high school student in 1979, four years before the events of X-Men: Apocalypse occurred. To put it plainly, figuring out Cyclops' age is a pretty challenging endeavor.

17 MAGNETO AND PROFESSOR XAVIER'S FRIENDSHIP

Magneto and Professor Xavier have been friends for many years, but their relationship hasn't been necessarily consistent. In X-Men, Charles Xavier revealed that he had met Magneto when they were both 17 years old. In X-Men: First Class, however, it's established that both met as adults. Things got a bit more confusing in X-Men: The Last Stand.

In the movie, Xavier and Erik are shown to be friends during the '80s, when they pay a visit to a young Jean Grey to help her with her powers. X-Men: First Class also retconned that bit of lore, revealing that Xavier and Magneto had parted ways in the early '60s, after Magneto accidentally paralyzed Charles.

16 MOIRA MACTAGGERT

Moira MacTaggert played a pivotal role in the prequel X-Men trilogy. In X-Men: First Class, the CIA agent helped Charles Xavier and his superhero group defeat the Hellfire Club. Then, in 2016's X-Men: Apocalypse, she helped Charles once again in his fight against the movie's eponymous villain. Moira forged a strong bond with Xavier, and quickly became one of his most trusted allies.

Unfortunately, her role in the franchise has left a few fans more than a bit confused. You see, Moira MacTaggert first appeared in X-Men: The Last Stand, which established her as a 30-something year old doctor caring for Charles Xavier's twin brother. Seeing how Moira was already around 30 in the '60s, it leaves us wondering how she remained so young for over four decades.

15 CEREBRO'S ORIGIN

Charles Xavier isn't alone in his quest to help mutants. He's assisted by Cerebro, a powerful machine able to locate any mutant in the world. In X-Men, Professor Xavier mentioned that he had built the mind-reading machine with the help of Magneto, back when they were still friends with each other. It was an interesting bit of lore for the X-Men franchise, but one that didn't last long.

In X-Men: First Class, Beast is the man behind the creation of Cerebro. In fact, Charles doesn't come into contact with the machine until it's fully operational. Sadly, Magneto helping Xavier build his in-home Cerebro seems almost impossible, seeing how the two had a falling out before construction on the machine could even begin.

14 EMMA FROST'S HISTORY

Emma Frost is one of the main baddies in X-Men: First Class. The character is introduced as a trusted member of the Hellfire Club, but she ultimately allies herself with Magneto. Unfortunately, Frost didn't enjoy a long tenure in the X-Men franchise after the film. During a 1973-set sequence in Days of Future Past, Magneto reveals that Emma passed away at some point after the events of First Class.

This bit of information is confusing, seeing how Frost appears alive in the third act of X-Men Origins: Wolverine, which is set six years after Emma's demise. Understandably, this apparent continuity error left a few fans scratching their heads. Fortunately, producer Lauren Shuler Donner cleared up the matter, revealing that there was no connection between both Emmas.

13 ANGEL'S AGE

Angel first flew into the big screen with X-Men: The last Stand, played by Ben Foster. The character was portrayed as a young, 20-something year old man grappling with his mutant abilities. Ten years after The Last Stand hit theaters, Angel was reintroduced in X-Men: Apocalypse as a young fighter in an underground mutant fight club.

Seeing the character again was exciting, but his new role made little sense continuity-wise. In The Last Stand, it's implied that Angel was born around the '80s. That creates a problem, since Apocalypse shows him as a teenager in the '80s. Sadly, the time-changing shenanigans of Days of Future Past don't play a factor in this, given how Apocalypse's Angel was born before the events of that film.

12 THE ORIGIN OF MAGNETO'S HELMET

Magneto's helmet has been an important part of the character for many years. The helmet has been prominently featured in the X-Men franchise, but its history is a bit... well, confusing. In X-Men, Charles Xavier learns about the helmet for the first time after Magneto uses it to block his psychic powers.

In X-Men: First Class, however, Erik puts on the helmet for the first time in the '60s, after he steals it from Sebastian Shaw. Charles is immediately aware of this, as Magneto puts it on to keep him out of his head while he gets revenge on Shaw. Given how traumatic that ordeal was for Xavier, it's tough to imagine how he didn't remember the helmet in X-Men.

11 PSYLOCKE

Psylocke was brought to the X-Men franchise in X-Men: The Last Stand. In the movie, she's portrayed as a young woman who allies herself with Magneto's Brotherhood of Mutants. Sadly, the character isn't given much time to shine, since she's downed by Jean Grey during the movie's third act. Fortunately, Psylocke resurfaced in X-Men: Apocalypse, played by Olivia Munn.

The character was relatively well-received by audiences, but as some diehard fans may have noticed, her appearance didn't make much sense timeline-wise. You see, Apocalypse is set in the '80s. Given that, it's tough to imagine how Psylocke could have been an adult by the '80s, and later resurface as a 20-something year old in X-Men: The Last Stand, which is set in the mid '00s.

10 MYSTIQUE AND PROFESSOR XAVIER'S FRIENDSHIP

X-Men: First Class established a strong connection between Charles Xavier and Mystique. The two mutants met at a young age and quickly developed a friendship that led to them becoming surrogate siblings. Their friendship became an important part of the X-Men franchise, and even played a big part in numerous films. Weirdly, their relationship was nowhere to be seen in the original trilogy.

Charles and Mystique crossed paths a few times over the franchise's first three movies, but they barely acknowledged each other. Instead, both seemed quite indifferent toward one another. The friendship was finally brought up by Charles Xavier's future version in Days of Future Past. Sadly, the scene didn't offer an in-story explanation for their previously-indifferent interactions.

9 EVERYTHING ABOUT BOLIVAR TRASK

X-Men: The Last Stand introduced audiences to Trask, the Secretary of Homeland Security, played by Bill Duke. Even though his first name was never actually mentioned, the character was largely assumed to be the live-action version of Bolivar Trask, a powerful X-Men villain responsible for the creation of the Sentinels in the comics.

The character received a makeover in X-Men: Days of Future Past, where he was portrayed by Peter Dinklage. Dinklage's Trask was a completely different version of the one played by Bill Duke in terms of appearance, motivations and personality. Furthermore, his existence in the '70s made it even tougher to understand his role in the present-set The Last Stand. Ultimately, it's easier to see the two Trasks as completely different characters.

8 COLOSSUS' APPEARANCE

Colossus got a new chance at big screen stardom with Deadpool. The film delivered a surprisingly faithful adaptation of the character, and audiences embraced his appearance, humor and distinctive personality. As some fans may have noticed, though, Deadpool's interpretation of Colossus presented a big inconsistency in the X-Men saga.

Prior to Deadpool, Colossus had been featured in X2, The Last Stand and Days of Future Past. In said films, he was portrayed as a relatively slender individual with an American accent. Deadpool, however, turned Piotr into a much larger fella with a thick Russian accent, leaving fans to wonder what had happened to the previous version of the character.

7 CHARLES XAVIER'S PARALYSIS

Much like his telepathic abilities and genius-level intelligence, Charles Xavier's paralysis has been an important part of the character for many years. Unfortunately, the X-Men franchise hasn't exactly been consistent with it. In a flashback scene in X-Men: The Last Stand, it's shown that Xavier still had use of his legs during the '80s.

To fans' surprise, however, Xavier's disability was retconned five years later, in X-Men: First Class. The film, which took place in the '60s, established that Charles lost the use of his legs in his youth, after a stray bullet deflected by Magneto hit his spine. The scene was powerful and emotional, but it created a pretty big plot hole in the franchise's continuity.

6 THE X-MEN'S ORIGINS

In 2000's X-Men, Wolverine is taken to the X-Mansion after being knocked out by Sabretooth. Once there, he's greeted by Charles Xavier, who explains the history of his school in an effort to get the confused hero acquainted with his new environment. During their chat, the beloved professor mentions that Cyclops, Jean and Storm were some of his first students.

That piece of information was later contradicted in X-Men: First Class. The film saw Xavier taking a group of young mutants under his wing to prepare them for a fight against Sebastian Shaw. By the end of the movie, Charles officially opens his school, welcoming a number of different mutants years before meeting Scott Summers, Storm or Jean.

5 WOLVERINE'S RELATIONSHIP WITH SABRETOOTH

Wolverine's relationship with Sabretooth was at the forefront of X-Men Origins: Wolverine. The film established the pair as brothers who looked after each other for hundreds of years after running away from home. Even though the movie wasn't necessarily well-received, Logan and Sabretooth's relationship became one of the most resonant pairings in the X-Men franchise.

Sadly, their bond loses a bit of impact when we consider the fact that it doesn't really fit into the overall X-Men continuity. You see, X-Men pitted Wolverine against Sabretooth, Strangely enough, neither of them acknowledged their relationship. Now, it was understandable for Wolverine to not remember their shared past, the same couldn't really be said for Sabretooth.

4 JEAN GREY'S FLUCTUATING AGE

Jean Grey made her triumphant return to the X-Men franchise in X-Men: Apocalypse. Sophie Turner delivered a gripping portrayal of the character, and she established Jean Grey as one of the most fascinating characters in the X-Men series. As diehard fans of the franchise may have noticed, however, her appearance also created a considerable plot hole in the saga.

X-Men: The Last Stand featured a flashback sequence in which Charles Xavier and Magneto paid a visit to a young Jean Grey to talk about her powers. That's where the continuity issue comes in. In The Last Stand's 1982-set sequence, Jean Grey is just a child. However, Jean is already a teenager in Apocalypse, which is set in 1982.

3 JUGGERNAUT'S FAMILY TIES

In the comics, Juggernaut is Charles Xavier's stepbrother. Their relationship is officially established in the X-Men franchise in Deadpool 2, when Juggernaut identifies Charles as the reason behind his signature helmet. The easter egg was a nice nod to the characters' long (and incredibly complicated) comic book history, but it also presented a minor issue in the X-Men film timeline.

Juggernaut made his big screen debut in X-Men: The Last Stand. In that movie, the villain crossed paths with Xavier during a conflict between Magneto's Brotherhood of Mutants and the X-Men outside of Jean Grey's childhood home. Weirdly enough, neither Charles nor Juggernaut never acknowledged each other, leading fans to believe there wasn't any real connection between them prior to Deadpool 2.

2 WOLVERINE'S WEAPON X PROCEDURE

As part of the Weapon X program, Wolverine had his skeleton coated with Adamantium and his memory erased. After years of searching for answers, Logan came close to finding out more about himself in X2, courtesy of William Stryker, the man behind the Weapon X procedure. During the movie's second act, Stryker invades the X Mansion and comes face-to-face with Logan.

As they talk, Stryker reveals that it's been 15 years since Wolverine got his metal claws. Interestingly, that seemingly throwaway line presents a continuity issue for the X-Men series. In X-Men Origins Wolverine, Logan gets his Adamantium skeleton in 1979. The original X-Men trilogy takes place in the early '00s, meaning that, according to Stryker, Wolverine should have gotten his claws around the mid to late '80s.

1 INEXPLICABLE LONGEVITY

Each installment in the X-Men prequel series takes place ten years after its predecessor. First Class is set in the '60s, Days of Future Past is (partly) based in the '70s and Apocalypse takes place in the '80s. Weirdly, however, none of the characters in the franchise have actually aged despite the 20-year gap between First Class and Apocalypse.

By Apocalypse, both Charles and Erik are in their '50s, yet still look like 30-year-old men. Same goes for Beast and Havoc. While their slow aging process could be attributed to their mutation, things get a bit confusing when we take into account that Moira MacTaggert, a normal human, looks like a 30-year-old in the '80s, despite being in her '50s.