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The term undead describes beings in mythology, legend or fiction that are deceased yet behave as if alive. A common example is a corpse re-animated by supernatural forces by the application of the deceased's own life force or that of another being (such as a demon). Undead may be incorporeal like ghosts, or corporeal like ghouls, vampires and zombies. The undead are featured in the belief systems of most cultures, and appear in many works of fantasy and horror fiction.
Bram Stoker considered using the title The Un-Dead for his novel Dracula (1897), and use of the term in the novel is mostly responsible for the modern sense of the word. The word does appear in English before Stoker but with the more literal sense of "alive" or "not dead", for which citations can be found in the Oxford English Dictionary. Stoker's use of the term refers only to vampires, and the extension to other types of supernatural beings arose later. Most commonly, it is now taken to refer to supernatural beings which had at one time been alive and continue to display some aspects of life after death, but the usage is highly variable.
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The dead lovers
, ca. 1470
Frankenstein by Mary Shelley is a seminal text in 19th century discourse about the undead. Published in 1818, it was based on a number of sources, including Ovid's myth of Prometheus (indeed, the novel is subtitled "The Modern Prometheus"), Milton's Paradise Lost, Coleridge's The Rime of the Ancient Mariner, and William Beckford's Gothic novel Vathek. Shelley also drew on European folklore, such as the medieval Jewish legend of the golem, and German, Czech and Moravian ghost stories featuring vengeful dead (many of whom have characteristics of vampires rather than zombies).
Later notable 19th century stories about the avenging undead included Ambrose Bierce's The Death of Halpin Frayser, and various Gothic Romanticism tales by Edgar Allan Poe. Though their works could not be properly considered zombie fiction, the supernatural tales of Bierce and Poe would prove influential on later writers such as H. P. Lovecraft, by Lovecraft's own admission.
Forms of undead 
The Living Corpses
In Dungeons & Dragons and similar systems, clerics can attempt to "turn" undead by invoking their patron deities or channeling "positive energy" (other-dimensional life energy, which animates and heals living creatures, and is the antithesis of negative energy, which animates and heals undead creatures.) This forces the undead creature away from the cleric; powerful clerics are capable of completely destroying weaker undead creatures with this ability. Although the act of turning away the undead relies primarily on power of faith, a holy symbol is usually required as a focus for the divine power being invoked. Clerics of evil gods can rebuke and control the undead in a similar fashion, by instead channeling "negative energy".
In other games, such as Final Fantasy, undead can be damaged by using magical effects that heal normal living beings. Items or magic that revive dead characters will often destroy undead completely.
See also