In Deadpool 2, the time-traveling mutant played by Josh Brolin is Cable.
Cable is a soldier from a dystopian future who travels to the past to kill a young mutant named Russell Collins, also known as Firefist. Deadpool assembles the X-Force to protect Russell, creating the central conflict of the film.
Cable’s comic-book identity is Nathan Summers, the son of Scott Summers, or Cyclops, and Madelyne Pryor in Marvel Comics. His film backstory differs in details but retains the idea of a time-traveling soldier with advanced technology and a cybernetic arm.
Deadpool 2 was released in 2018 and directed by David Leitch. Josh Brolin also played Thanos in Marvel Studios films, but Cable and Thanos are separate characters. Brolin’s casting created a notable connection between two different Marvel film franchises, even though the characters belong to different fictional universes.