In folklore, doppelgangers are sometimes written in text as one who casts no shadow and possesses no reflection in a mirror or body of water. When they shadow a person, they are supposed to serve as a confidante and give advice, but in many cases, the advice is misleading or ill-willed , meant to place the person in danger or humiliating circumstances.
In rare times, the doppelganger will place ideas in the heads of their victim's , appearing to their family and friends and causing confusion by acting irrational. This is seen in the movie with Drew Barrymore (mentioned in the article, "What is a Doppelganger?") when she attends a party and seductively dances with her roommate (which seems very much out of her character). In German belief, a doppelganger doesn’t even have to be a person and may manifest as the opposite gender or an animal.
Over the years, there have been well-known accounts regarding various encounters with doppelgangers. One of the most notable involves Percy Shelley, a poet and atheist of English blood, who on July 8th, 1822 drowned in the Bay of Spezia situated close to Lerici. On August 15th, during a stay in Pisa, Mary Shelley penned a letter to another explaining the accounts told to her by Percy that he had come in contact with his own doppelganger. The story begins a week after Mary suffered a near fatal miscarriage that Percy had a nightmare about the residence falling into a flood. He saw that the next morning he would see a vision of himself on his terrace and would have a talk with him.
The concept of the doppelganger appears in one of Percy Shelley's dramas , titled Prometheus Unbound (1820), which offered a revealing passage In Act I, he wrote, "Ere Babylon was dust, / The Magus Zoroaster, my dear child, / Met his own image walking in the garden. / That apparition, sole of men, he saw. / For know there are two worlds of life and death: / One that which thou beholdest; but the other / Is underneath the grave, where do inhabit / The shadows of all forms that think and live / Till death unite them and they part no more...."
John Donne was an English metaphysical poet who is believed to have seen his wife's doppelganger in 1612 in Paris, which happened to be the same night he experienced the stillbirth of a baby girl. He would reveal that he would see a vision of his wife two times , holding a dead child in her arms. He then went on to say that she vanished after looking back at his face. In 1675, a book called "Life of Dr John Donne" would make first mention of this event, making a point that he was unaware of the stillbirth when it took place despite seeing the visions.
Carl Sandburg once wrote that Lincoln was haunted by an odd dream or illusion that when he looked into the mirror, he would see "two faces" of himself. It was said that he was haunted by these "faces" in the mirror and that he even shared his worry with his wife. He described the way the faces were different and displayed varied characteristics. She replied that one of the faces meant he would be elected to a second term of presidency and that the death "look" of the other face meant he would not live through the second term. It is believed that this story was confirmed by Mary Todd Lincoln.
Curiously, it is also known that Lincoln carried about superstitious ways and that his tendency to look into old mirrors may have caused the double imagery, which was commonplace with these sorts of objects of the time. This is what makes it suspect whether or not Lincoln actually entered a doppelganger, even though his wife's assessment was eerily coincidental.