Doppelgänger (Dungeons & Dragons)

In the Dungeons & Dragons fantasy role-playing game, Doppelgängers are monstrous humanoids, infamous for their shapeshifting abilities, which allow them to mimic almost any humanoid creature. In D&D, doppelgängers are lazy but cunning creatures, who kill or dispose of people then assume their place. They are not downright evil, but extremely self-centered and liable to look down on their victims. In their true form, doppelgängers appear as tall, elfin, gray-skinned humanoids, whose thin bodies make them appear (to human eyes) sexless. Even this form is deceptive, since it has no visible muscle mass, suggesting they are physically unfit, when in fact they are quite strong and agile.

Doppelgängers hate working, and so usually assume the forms of people who are well off in society, commonly working in groups so as to be able to replace the entire family and leave the servants working for them. Doppelgängers are believed to be an artificial race, created by some mad wizard, and to this day have a fondness for working with the magically inclined; mainly being used as assassins or in elaborate plots to usurp power.

Doppelgänger families tend not to be close; usually a male and female meet, engage in casual sex, then leave one another, with the female being forced to single-handedly rear any resulting newborns&mdash;who will leave their mother upon reaching maturity. Some doppelgängers, however, form tightly knit family clusters, while others will mate with humanoids, taking malicious delight in using their non-doppelgänger spouse as a cover for their inhumanity. Children born of such unions have a chance of being a half-doppelgänger.

Doppelgängers in other campaigns
In the Eberron campaign setting, there is a race descended from half-human/half-doppelgangers, known as Changelings. They cannot dramatically change shape as their nonhuman ancestors, but are nonetheless massively proficient at disguise. They are commonly rogues and have that as their favored class.

Dread Doppelgängers
A subspecies of doppelgänger can be found in the Demiplane of Dread, Ravenloft. These dread doppelgängers, like many Ravenloftian creatures, are a twisted rendition of the original. Dread doppelgängers are capable of mimicking with 100% efficiency as well as generating natural illusions via their "Glamer" ability, but in the process have become sexless parasites, dependent on their ability to integrate with society to survive. While normal doppelgängers have their own culture and have no real need to mingle with humanoids, Dread Doppelgangers can only reproduce by mating with humanoids (usually doing so as males, as a "pregnant" dread doppelgänger cannot change forms until after giving birth) and have effectively lost their own culture.

Dread doppelgängers have one major accomplishment over their natural kin: their own country. The Ravenloft domain of Paridon is the birthplace of the dread doppelgänger, and as such is crawling with the vile things. The Darklord of the domain, Sodo the Flickerflame, directs and organizes a vile ritual called the Blood Rite, which takes place once every thirteen years and is used by Sodo to give himself effective immortality. This ritual is conducted by a chosen dread doppelgänger, and is referred to by the Paridoners as "The Bloody Jack Killings" because for many years Paridon thought the killings were the work of a madman.

Doppelgängers in 3rd Edition
In the 3rd edition of Dungeons & Dragons, Doppelgängers were classified as shapechangers. When this creature type was made obsolete in 3.5 Edition, their type was changed to Monstrous Humanoid.