Since Walker died in a car crash in 2013 with only some of his scenes in the can, the guy we see gallivanting on screen for a good deal of the movie is a concoction of body doubles (including Walker's two brothers) and CGI, courtesy of Peter Jackson's visual effects company Weta D?igital.

Technology has been used to snatch celebrities back from the afterlife for quite a while, sometimes for promotional ends, but also in order to finish up earlier movies whose main stars have died during production—the archetype being  ?The Crow's Brandon Lee. Lee was accidentally killed on set in 1993, and was replaced for the final scenes by another actor onto whom a digital reconstruction of Lee's face was grafted. 

But what so far has been a last resort could one day become routine. According to special effects experts, actors are starting to stockpile digital 3D replicas of themselves in order to keep appearing in movies after death.