The Stranger, the ghostly figure who picks up Seeger and delivers him back to Malpais in episode seven, is an echo or a remix of several figures throughout literary and holy texts. He is, possibly, the most folkloric figure within Perdition's Teeth: more rooted in the American -- and, admittedly, some older -- legends than many of the other characters.
The most obvious is that the Stranger is an inversion of the classic "Vanishing Hitchhiker" trope. According to Folklorist Jan Harold Brunvand of the University of Utah, in the book The Vanishing Hitchhiker: American Urban Legends and their Meaning is
the classic automobile legend. The returning-ghost tale was known by the turn of the [twentieth] century both in the united states and abroad. It acquired the newer automoile motif by the period of the Great Depression and therafter spawned a number of subtypes with greatly varied and oddly interlocking details, some of which themselves stemmed from earlier folk legends (Brunvand 24)
Brunvand labels several essential elements -- the driver, the night setting, the hitchhiker, the destination, the disappearance, the driver's curiosity, and the identification of the driver -- and our version remixes these: the ghost is the driver, and the destination is unspoken. This fundamentally changes the nature of the tale because, like many ghost stories in the American folkloric canon this one is about returning home: a psychological unexploded bomb left over by the Civil War and exacerbated by the great migration during the dust bowl: we Americans are forever alienated from our roots, even when we don't go that far from them.
This motif is so common that Brunvand goes on to report fifteen variations directly, and comments that it "is the only urban legend with a specific motif number assigned to it in the standard folkloristic reference works" (41).
Another figure from Brunvand's studies which might be analogous, though from somewhat later, is the "ghost trucker" who are noted to "roll on night after night like eighteen-wheel diesel Flying Dutchmen" (179): here, after all, the ghost has its own vehicle and might provide aid to the living human protagonist.
This may strike some as a bit gauche, but I cannot read about a "ghost trucker" and not think about the classic "Large Marge" scene from Pee-Wee's Big Adventure (1985), where Alice Nunn plays a frightening, standoffish ghost who nonetheless gets the titular man-child further down the road on his personal journey.
There are other possibilities -- such as that the Stranger is an earthbound angel, or Cain, or the the Rabbinic Acher -- but the resonance with the figure of the vanishing hitchhiker is unmistakable, and we're going to leave it at that. Oftentimes, questions are more interesting than answers, even if they aren't terribly satisfying.
Meta-textually, it may have simply been fitting: as the lead writer, I'm the one who put the characters into this situation, and play the narrator. On the other hand, as the engineer and producer, Alex gets the show finished and closer to production, and plays the stranger. It's a nice bit of symmetry.