There are several different kinds of Doppelgänger – over the years the word has grown so it encompasses almost any kind of double/duplicate being. The Doppelgänger may appear as a wispy, pale shadow or reflection, or take the form of a flesh and bone human being. It may choose to impersonate its human counterpart to the individual’s friends and family, behaving in a negative fashion. This causes great confusion, particularly when such convincing behaviour and advice is imparted from what could be considered “The Evil Twin.” The Doppelgänger may appear as a result of sorcery; through a magic spell cast to separate the physical self from its spiritual presence. In literature Doppelgängers have appeared in stories involving parallel worlds for time travel, representing an older or younger version of the central character in the story.

As well as being considered an omen of death, a Doppelgänger, like the horror genre’s iconic Vampire character, is said to have no shadow and no reflection. Mischievous and malicious, they like to stand just behind their human double, out of sight. The word is also used to describe the sensation of having glimpsed oneself in peripheral vision, in a position where there is no chance that it could have been a reflection. Think about all those times when you’ve seen something moving in the corner of your eye, but when turning around for a clearer look there’s nothing there…

Dogs and cats are supposed to be sensitive to a Doppelgänger’s presence, reacting when they see one; it seems that while the Doppelgänger can select which humans may see it, it has no control over an animal’s supposed extra sensory perception. A Doppelgänger is happy to listen to a human’s concerns and fears, sometimes giving bad advice and planting negative ideas into the subject’s mind.

Historical accounts of people seeing their own Doppelgänger include:

Queen Elizabeth I walked into her bedroom one afternoon, and was shocked to see herself lying on her bed. She died a short time later.
English poet Percy Bysshe met his Doppelgänger while in Italy, watching in alarm as the creature silently pointed towards the Mediterranean Sea. No long after this experience, Shelley drowned in a sailing accident in the Mediterranean Sea just before his 30th birthday.
English poet John Donne encountered his pregnant wife’s Doppelgänger during a visit to Paris. The image was holding a newborn baby. At the exact moment Donne’s wife gave birth to a stillborn child.
US President Abraham Lincoln caught his reflection in his mirror just after the 1860 election. The image showed two faces; one face was considerably paler than his own reflection. He saw this twice more, and when he told his wife about it she predicted it meant he would be elected for a second term, but the paler face meant he would not live through his second term. On 14 April, 1865, Lincoln was assassinated.

Here are some ways horror writers have used the Doppelgänger to great effect:

Stephen King’s The Dark Half tells of a writer named Thad Beaumont, who writes gory crime novels under the pen name George Stark. Beaumont’s own novels aren’t nearly as successful as those of his alter ego, and when the truth about Stark’s identity is revealed, Beaumont decides it’s time to get rid of George. A mock funeral is conducted, complete with the epitaph “Not a Very Nice Guy”. But George refuses to die, and comes back looking for vengeance…

Edgar Allan Poe’s William Wilson meets a boy at school almost identical in appearance to himself. They speak in similar tones, and share the same birthday as well as the same name. Over time the boy becomes an exact copy of William Wilson, until it is impossible to distinguish between the two. When William realises the boy’s face has become a mirror image of his own he leaves school in panic. He later learns the other William also left school, and as he grows older finds the other William is always with him, alerting others to Wilson’s deteriorating principles and morals.

Anthony Horowitz’s Point Blanc offers a twist on the Doppelgänger, describing how the head of an exclusive school for troubled sons of wealthy and powerful men uses his clones to infiltrate his pupils’ families in order to take control of their empires.

Dean Koontz’s Mr Murder is about writer Marty Stillwater, who realises there are periods during his daily life when he cannot recall what he was saying or doing. At the same time a killer is out on the streets, and finds himself mysteriously drawn towards the Stillwater’s home. The killer murders many people while trying to get to the Stillwater family, believing they belong to him. While hunting the killer the authorities realise he is identical in appearance to Marty Stillwater, and when they learn he’s removed his tracking device the truth is revealed…

Imagine for an instant if there was another YOU living somewhere in the world. Not only is this other YOU identical in physical appearance, he/she has lived a life in the exact circumstances as yours. Know the same “people” you do… has the same habits and thought processes. Can two people who’ve never met be mirror images of one another, living simultaneous and identical lives? Is this individual a replica of you, or is he/she your Doppelgänger? Or… perhaps YOU are the replica’s Doppelgänger. It’s an interesting idea…