While most people associate Deadpool with the world of the X-Men, Wade has always been something of an outsider among the superhero team. This is partially because he’s incredibly hard to work with, but it’s also because the Merc with a Mouth isn’t technically a mutant. So why does everyone think he is? Deadpool himself blames the movies.
Ryan Reynolds led the antihero to gross over a billion dollars at the box office, and in doing so, jettisoned the character into newfound popularity... but did so without changing the nature of the source material. Reynolds’ Deadpool retains the sarcastic, raunchy, fourth-wall-breaking humor of the comics. However, something that the filmmakers did change is Deadpool’s relationship with the X-Men. In the movie, Deadpool repeatedly turns down Colossus’s offer to join the team, and doesn’t hold back from making fun of them and their confusing X-Men timelines. But in the comics it's the reverse: the X-Men want nothing to do with the non-mutant Wade.
In the new Deadpool #6 by Kelly Thompson, Wade - who recently became the King of the Monsters and took over Staten Island, as he does - goes on a rant about how the X-Men won’t let him into Krakoa, the sovereign nation for mutants. Why? Because no matter what the films may confuse, the comics know Wade isn't a mutant at all.
Interestingly, while Deadpool blames the movies for making people believe he’s a mutant, he’s technically not a mutant there, either. A mutant is somebody born with an active x-gene in other words, born with powers. Wade had to have his x-gene activated through experiments, which makes him something called a mutate, or someone who got their powers later in life via some kind of transformative event (like being bitten by a radioactive spider). So Deadpool isn’t a mutant in the comics or the movies. Well, unless you count the version in X-Men Origins: Wolverine, whose mutant power is being really good with swords(?).
Unfortunately for Wade, the X-Men don’t take too kindly to him sneaking onto their mutant paradise later in the issue, leading to a fight that sees Deadpool forced to leave. He’s told that he would be welcome to visit if he went through the proper channels. But the 'proper channels' aren’t really his style, which is why fans love him - even if the X-Men don’t.