A doppelgänger (; German: ['d?pl], literally "double-goer") is a non-biologically related look-alike or double of a living person, sometimes portrayed as a ghostly or paranormal phenomenon and usually seen as a harbinger of bad luck. Other traditions and stories equate a doppelgänger with an evil twin. In modern times, the term twin stranger is occasionally used. The word "doppelgänger" is often used in a more general and neutral sense, and in slang, to describe any person who physically or behaviorally resembles another person.
The word doppelgänger is a loanword from the German Doppelgänger, a compound noun formed by combining the two nouns Doppel (double) and Gänger (walker or goer). The singular and plural forms are the same in German, but English usually prefers the plural "doppelgängers". The first known use, in the slightly different form Doppeltgänger, occurs in the novel Siebenkäs (1796) by Jean Paul, in which he explains his newly coined word by a footnote - while actually the word Doppelgänger also appears, but with a quite different meaning.
Like all nouns in German, the word is written with an initial capital letter. Doppelgänger and Doppelgaenger are essentially equivalent spellings, and Doppelganger is different and would correspond to a different pronunciation. In English, the word should be written with a lower-case letter (doppelgänger) unless it is the first word of a sentence or part of a title. It is further common to drop the umlaut on the letter "a", writing (and often pronouncing) "doppelganger".
English-speakers have only recently applied this German word to a paranormal concept. Francis Grose's, Provincial Glossary of 1787 used the term fetch instead, defined as the "apparition of a person living." Catherine Crowe's book on paranormal phenomena, The Night-Side of Nature (1848) helped make the German word well-known. However, the concept of alter egos and double spirits has appeared in the folklore, myths, religious concepts, and traditions of many cultures throughout human history.
In Ancient Egyptian mythology, a ka was a tangible "spirit double" having the same memories and feelings as the person to whom the counterpart belongs. The Greek Princess presents an Egyptian view of the Trojan War in which a ka of Helen misleads Paris, helping to stop the war.. This is depicted in Euripides' play Helen. In Norse mythology, a vardøger is a ghostly double who is seen performing the person's actions in advance. In Finnish mythology, this is called having an etiäinen, "a firstcomer". The doppelgänger is a version of the Ankou, a personification of death, in Breton, Cornish, and Norman folklore.
German playwright Goethe described an experience in his autobiography Dichtung und Wahrheit in which he and his double passed one another on horseback. In addition to describing the doppelgänger double as a counterpart to the self, Percy Bysshe Shelley's drama Prometheus Unbound makes reference to a dead child who "met his own image walking in the garden".Lord Byron uses doppelgänger imagery to explore the duality of human nature.
Fyodor Dostoyevsky's novel The Double presents the doppelgänger as an opposite personality who exploits the character failings of the protagonist to take over his life. Charles Williams' Descent into Hell (1939) has character Pauline Anstruther seeing her own doppelgänger all through her life.Clive Barker's story "Human Remains" in his Books of Blood is a doppelgänger tale, and the doppelgänger motif is a staple of Gothic fiction.
With the advent of social media, there have been several reported cases of people finding their "twin stranger" online, a modern term for a doppelgänger. Twinstrangers.net is a website where users can upload a photo of themselves and facial recognition software attempts to match them with another user of like appearance. The site reports that it has found numerous living doppelgängers--including three living doppelgängers of its founder Niamh Geaney.
Heautoscopy is a term used in psychiatry and neurology for the hallucination of "seeing one's own body at a distance". It can occur as a symptom in schizophrenia and epilepsy, and is considered a possible explanation for doppelgänger phenomena.
Criminologists find a practical application in the concepts of facial familiarity and similarity due to the instances of wrongful convictions based on eyewitness testimony. In one case, a person spent 17 years behind bars persistently denying any involvement with the crime of which he was accused. He was finally released after someone was found who shared a striking resemblance and the same first name.
In one of the stranger twists of fate in literary history, Jean Paul coins two terms in Siebenkäs, "Doppelgänger" and "Doppeltgänger." The term Jean Paul uses to describe Siebenkäs and Leibgeber is "Doppeltgänger," which he defines in a footnote: "So heißen Leute, die sich selber sehen" ["the name for people who see themselves"] (2, 67). Earlier in Siebenkäs the neologism "Doppelgänger" also appears for the first time and means something quite different. In a description of the wedding banquet in the first chapter, the food is so delicious and abundant that "not only was one course [Gang] served but also a second, a Doppelgänger" ["nicht bloß ein Gang aufgetragen wurde, sondern ein zweiter, ein Doppelgänger"] (2, 42). "Gang" in German has multiple meanings, ranging from a "walk" to the "course" of a meal; according to Jean Paul, when people "see themselves," when one "goes twice," one is a "Doppeltgänger"; when one has a meal of two courses, in which the second doesn't come second but together with the first, this is a "Doppelgänger."