https://www.cnet.com/news/who-is-deadpool-2-cable-everything-you-need-to-know/

Deadpool 2 features Josh Brolin as Cable, a super soldier who spends most of his time shooting and scowling. The movie hints at Cable's complex comics backstory, but mostly keeps things simple. It establishes him as a tragic time traveler with a metal arm and a light-up laser eye. If you've just come out of Deadpool 2 wondering why Cable has any of that going on, you may want to sit down. The answers are going to be more than a little complicated, and no, they aren't covered by Deadpool's post-credit scenes.

And yes, there will be some spoilers for Deadpool 2 here. Proceed with caution!