Originally Posted by X-Maniac
Characters are often chosen for reasons other than whether they were in the original story. As happened in First Class, where Havok, Banshee, Angel Salvadore, Azazel, Emma Frost and Riptide found themselves part of Xavier/Magneto's early years.
Those characters were chosen because they provided cool visuals, or a good match for an opposing mutant on the other team, or because they didn't contradict the timeline of the original trilogy.
Warpath could be in the movie for any number of narrative reasons. He might be there as an opponent for Beast or Colossus, or to provide his powers to Rogue so she can kick butt at last.
It's also worth bearing in mind that there is a native American mutant (wearing blue and red) is seen briefly in the animated X-Men episode Slave Island, where a whole load of mutants including some X-Men have been captured and imprisoned on Genosha to help power a Sentinel factory. We see Mastermind completed and see Bolivar Trask, Gyrich and others. That same native American mutant is glimpsed in the opening credits of the 90s animated series, on Magneto's team. It must be either Thunderbird or Warpath.
Also, in the Exiles comic book, Thunderbird is a member of that group, along with Blink (who is also in this film). They are tasked with fixing damaged realities.
So there are various reasons and influences and inspirations that might be at work here. We just don't know enough about the story.
That was an alternate version of the original Thunderbird, John Proudstar, and the name on the movie set chair specifically said James "Warpath" Proudstar, so not the same.