In the folklore of Morocco, a Grine is the double of an existing person that lives in the spirit world.
Description
In Moroccan myth, each time a human is born in our world, a djinn called a Grine is born in another, adjacent world. The actions of the human inevitably influence the actions of the Grine, whereas the actions of the Grine inevitably influence those of the human.
Art/Fiction
Wayne Thomas Batson's The Door Within Trilogy features a race of humanoids called Glimpses, who dwell in a world adjacent to ours. Each Glimpse corresponds in action, appearance, character, birthdate, and time of death to a human that lives in our world. If a human travels to the Realm of the Glimpses, the corresponding Glimpse will disappear for as long as the human remains. Glimpses have white skin and eyes that change color according to their political alliance.
Source
Rose, Carol, Spirits, Fairies, Leprechauns, and Goblins, 1996.