So, let's talk Cable. He's the son of Cyclops and a clone of Jean Grey, from a future where the villainous Apocalypse (from X-Men Apocalypse, natch) rules the world and infects Cable with a "techno-organic virus." Cable keeps the virus in check by using his telekinetic powers, meaning he has to rely on guns in battle, which he does when he goes back in time (to the present) to try and make it so Apocalypse can never rise to power. Got all that?
Considering it takes a whole paragraph to explain the origins of a dude with as silly a name as "Cable," he was never really going to fit in easily with the rest of the more serious X-Men movie franchise. But bringing him to the big screen by way of Deadpool, allowing his ultra-serious attitude (and nonsensical origin) to be played for laughs, is a brilliant move. Even better is the fact that the duo even starred in a fan-favorite comic series called, quite aptly, Cable & Deadpool. There's plenty of material to work with here.