There's no question that the first "phase," to borrow a term from Marvel Studios, of the X-Men film franchise at 20th Century Fox revolved around the character of Wolverine. He was the only character to actually get a solo film (let alone three) out of the original cast, and Hugh Jackman's breakout performance as Logan put the X-Men on the movie map.
When the franchise received its soft reboot with X-Men: First Class, sure, Wolverine wasn't directly included (though he did have the best cameo and one-F-bomb-per-PG-13 rule usage ever); but to push that "Phase 2" forward, and to reconcile the two phases together, they told a time-travel story that centered on, you guessed it, Wolverine. And when it came time to truly put that story to rest, it was in a solo Wolverine movie, ending the tale of Logan and Professor X as started in 2000.
But the X-Men franchise isn't dead, and may even be on the cusp of a new level of thriving it hasn't reached yet, and that's thanks to a strange dark horse character: Deadpool. When Jackman announced he was leaving behind the role he'd played for over a decade and a half, speculation started to turn to who was next. The Marvel Cinematic Universe undoubtedly revolves around Robert Downey Jr.'s Iron Man, and the DCEU is certainly trying to revolve around Ben Affleck's Batman (just look at the number of Gotham and Bat-related movies in development if you have any doubt).
Enter Ryan Reynolds as Deadpool, a passion project that took 11 years from inception to release, and really only ever got made because of an internet leak that fans responded to in kind. Deadpool set records for the X-Men film franchise, for R-rated movies, and was by all accounts simply an immensely entertaining film. It was a surprise hit for Fox, and one that they no doubt sought to build off of immediately.
Moving forward, the X-Men franchise is going to expand dramatically -- even in the coming year we'll have Deadpool 2, New Mutants, and X-Men: Dark Phoenix all pulling things in different directions. But from Deadpool 2, we'll have X-Force, a film that with Reynolds producing, will now undoubtedly feature Wade Wilson more centrally than was originally planned when the film was first proposed several years ago. While the core "X-Men" films will continue to make their way from the past forward (each film has played with the classic Marvel Comics sliding time-scale, where approximately seven years go by in the background while only one goes by for the characters, a fun nod to the comics that allows them to play in different decades), the present-day story is now Deadpool's show. Spawning other films from Deadpool gives Fox something the MCU will likely never have: an R-rated sub-franchise (and one that will likely be the top earner, while the parent franchise pulls into a comfortable second place).
In building a "Phase 3" of the X-films, Fox is having their cake with the ongoing story of the youngest X-Men, while eating it too with Deadpool and his ilk. It's even possible New Mutants could be the connective tissue between the two, as it was spawned from X-Men comics, and in turn gave birth to X-Force on the printed page when Deadpool, Cable, and X-Force creator Rob Liefeld took control of the franchise in the 90s. We've already seen Deadpool re-invent Colossus and introduce a character like Negasonic Teenage Warhead, who we never would've guessed would hit the big screen in the first place.
What does this mean overall? It means we'll get more X-Men movies than ever before, with two viable franchises running side by side. It also means that Deadpool cannot possibly be undervalued, as he now has a full franchise riding on his shoulders. Beyond Deadpool 2 and X-Force, we could very well see other films spin out, carrying the irreverent tone and action-forward storytelling of the surprise hit into more films than we have even heard rumors about.