Spoiler warning: This post includes minor spoilers for “Deadpool.” Then again, with the movie’s box office you probably saw it anyway.
After wrapping Deadpool’s first solo outing on the silver screen, the creative team had a little fun with the obligatory post-credits sequence. In Buellerian fashion, Ryan Reynolds admonished the crowd for staying around after the conclusion. Next, he promised that a sequel is coming, and that Cable would be in it.
Both characters were created by Rob Liefeld, setting the bar for ’90s excess (X-cess?) in comics with their extreme violence, abundant pouches and overly huge muscles. The two were first brought together in New Mutants #98 (vol. 1), in which Deadpool tries to collect a bounty on Cable’s head.
Their dynamic was further explored in Cable & Deadpool, a series that saw the two come together as reluctant allies when they were infected by a deadly virus. After merging DNA in order to save themselves, the pair’s paths became more and more intertwined. Cable was hellbent on creating a utopian society through technology, while Deadpool contentedly stayed his wise-cracking self. As time wore on, Wade started to buy into Cable’s ideas and follow them a bit closer.
No matter what the two planned or what enemies they faced (and inevitably slaughtered), the series and the relationship were defined with humor and depth. Deadpool was a singular force of jokes, snide asides and witticisms, while Cable was an agent of dogged ideals. That is to say: The former always looked to have fun and the latter always saw that as a waste of time, always doing his best to stay focused on his mission.
Their mismatched personalities led to a classic buddy cop dynamic and eventually started to rub off on each other in unexpected ways. Deadpool became a bit more driven to see missions through; he adopted Cable’s vision and would even jeopardize his own well being to help his partner. This included betraying the X-Men in Cable & Deadpool #9 (pictured). 
For his part, Cable started to lighten up a bit and accept that he didn’t have to be so rigidly committed to his mission. Deadpool taught Nathan that caring for individuals instead of humanity at large is OK, as long as his heart’s in the right place. That’s why Cable went back to help Deadpool fight off Sabretooth: genuine compassion.
As with all great Marvel friendships, Civil War tore the two apart. Deadpool accepted a contract to hunt heroes and Cable stood against registration. After a debate and brief fight, the pair split up and headed down their own separate paths. They did manage to reunite and settle their differences once again before Cable sacrificed himself for Wade. (He got better.)
There’s no telling what Cable will be like on-screen. By the time he was paired with Deadpool for their series, the character had a huge mythology and identity that was ripe for some levity. Divorced from the X-Men and his grim origins, it’ll be interesting to see how Nathan can be translated without reams of exposition.
No matter the story, as long as Cable and Deadpool have grudging respect for each other and clashing personalities, the sequel will be worth waiting for.