Monster come in cycles. Werewolves wax and wane in and out of cultural visibility, and even vampires disappear and return. There might even be an end to zombie movies someday. Perhaps the current period will be known as the year of the doppelgänger. I am referring not only to Jordan Peele's brilliant Us, but also the return of the mirror universe in Star Trek: Discovery and Counterpart on Starz. If one wanted to add a literary reference one could include Ted Chiang's story "Anxiety is the Dizziness of Freedom." (I know that there might be more stories and novels, I just reading Exhalation now and cannot resist plugging it).