Comic books are filled with peripheral characters. It's the nature of the art. Your characters, A and B, need a crisis in order to use their super powers. Therefore, the writer creates C. C can be any number of things: a villain, a character in need of intervention, even an offspring of A and B who was sent to the future in order to save his life but has now returned with their own agenda. Some of these characters never make it about C status, some never make it out of that issue. This is the profile of one such character, whom, had it not been for some excellent writing and determination might have been relegated to the margins of A and B's biography.
Cable was a character who could have been very easily dismissed. He is the very picture of 90's excess that we associate with the Liefeld era. The man was devoid of personality, had a back story that makes Bill and Ted's Excellent Adventure sound plausible, and oh so many pockets. Cable ripped into the pages of the 90's X books wielding a gun the size of a coffee table, a glowing eye, and very loosely explained cybernetic implants. Cable should, by all rights, be appearing in the quarter bin with G.W. Bridge, Gen 13, and Maverick. Why is it then, that Cable has managed to sustain his own book in this far more discerning age of comics (thinks about last line, decides to leave it.)?
The first answer and the most obvious is his ties to the doomed Summers Legacy. Being the son of Cyclops and Jean Grey implants you in the Marvel U like few other things. Cyclops and Jean were often the characters we loved to hate growing up. In a house full of Wolverines and Icemen, they were the adults. Cyclops was the guy that told you not to jump on the couch and Jean was the woman who wasn't your mom but felt entitled to tell you to eat your vegetables. Yet their lasting appeal comes because despite all of their discipline, they are the two characters with the least control over their powers. When the glasses come off, Cyclops is a human hand grenade. The moment Jean really taps into her powers, she runs the risk of becoming a telepathic nuke. How can a guy with those two as parents not be compelling.
The real problem the Marvel U has had with Cable is finding his voice. Cable has infinite potential and infinite discipline. He has a Messiah Complex that tells him he can prevent the future that spawned him. He has his mother's compassion, his father's need for structure, but kept ending up keeping company with the most ludicrous of characters. Cable and Deadpool was fun, but it was always really Deadpool and Cable. So what is the voice of Cable?
Duane Swierczynski has given Cable the voice that makes him worth reading. The Cable of the current series is John Wayne with cybernetic implants, he's a telepathic Shane, he is that blond stranger who helps those in need, despite being just the sort of man that's after them. Swierczynski's Cable is a soldier without a country, dedicated only to the one Hope that can keep the world from being the way he knows it will be. See, the Nathan Summers I know is the one who is willing to give his very last breath to make sure he's never born.
He fights a war without end to prevent a war without end. This is Cable.