A survivor who can see and hear a Sentinel coming before anyone else, in a war where that is the only warning anyone gets.
James Proudstar is a mutant with enhanced strength, speed and senses, and one of the surviving mutants in the future. Booboo Stewart plays him.
Nobody in the future sequences is given a backstory, which is deliberate: they are the last ones, they have been doing this for years, and the film treats their competence as the only introduction they need.