The Passenger is a demonic road-stalker that preys on travelers who stop in the wrong places. It marks its victims with three slashes, tied to the hobo-code warning for “not safe here.” Once marked, the people themselves become the target, not just their vehicle.
The Passenger operates a bit like the entity from Lights Out: it cannot be in the light.
Its attacks are built around isolation, darkness, and travel hazards. It makes victims see things, manipulates cars and road equipment, and turns ordinary road-trip problems into traps: horns blare, doors open, lights go out, seatbelts tighten, jacks move, bolts vanish, and vehicles refuse to start. It can also physically attack, control a victim’s body, and take the form of a preacher.
The Passenger’s main weakness is St. Christopher, the patron saint of travel. Light burns it, a St. Christopher medal injures it, and a St. Christopher church is presented as a place of safety. (spoiler) Maddie ultimately destroys it by pinning it against the St. Christopher statue and impaling it with the statue’s staff, causing it to melt and burst into flames.
The Passenger seems to enjoy pulling the head back enough to expose the throat.
Follow the rules of the road, and he’ll leave you alone.