In ancient Greek literature, an eidolon (plural: eidola or eidolons) (Greek εἴδωλον: "image, idol, double, apparition, phantom, ghost") is a spirit-image of a living or dead person; a shade or phantom look-alike of the human form. The concept of Helen of Troy's eidolon was explored both by Homer and Euripides. However, where Homer uses the concept as a free-standing idea that gives Helen life after death, Euripides entangles it with the idea of kleos, one being the product of the other. Both Euripides and Stesichorus, in their respective works concerning the Trojan Horse, claim that Helen was never physically present in the city at all.
Walt Whitman's poem by the same name in 1876 used a much broader understanding of the term, expanded and detailed in the poem. In Whitman's use of the term we can see the use broaden to include the concept of an oversoul composed of the individual souls of all life and expanding to include the Earth itself and the hierarchy of the planets, Sun, stars and galaxy.
- In The Mark of Athena by Rick Riordan, three eidola appear as antagonists, possessing characters and making them fight against each other.
- In the short story "The White Ship" by H. P. Lovecraft the city of Thalarion in the Dreamlands is ruled by an eidolon named Lathi.
- In Clockwork Angel by Cassandra Clare, Tessa, the main protagonist is a 16-year-old girl whose father was an Eidolon, a shape-shifting demon. Tessa is a shape-shifter as well, though not a demon, and is told by a Silent Brother that she is Eidolon.
- The third part of "Helen in Egypt", the long poem by H.D. (Hilda Doolittle), is titled "Eidolon".
- In Ian Tregillis' Milkweed Triptych, the other-worldly entities responsible for magic are known as Eidolons.
- Beings called Eidolons appear in the series Book of the New Sun by Gene Wolfe.
- In the Wildstorm Comic "Stormwatch" by Warren Ellis, the Eidolon is a superpowered villain who travels the world telling people he's seen "the other side" and that there is no God. In reality he is actually just a disembodied ghost pining for oblivion.
- In The Wanderers by Meg Howrey, the astronaut-training simulation is named Eidolon.
- In The Secret Magdalene by Ki Longfellow the Greek concept of eidolon is discussed in detail throughout the book. Essentially, it is the heart of the story.
- In Worm by John McCrae, the second most powerful entity in the world is named Eidolon. He has the ability to hold multiple powers necessary for a given situation simultaneously.
- The Eidolon, a 1985 game by Lucasfilm Games.
- In the Magic: the Gathering plane of Theros, an eidolon is a spirit created when the soul of a dead person separates from its body.
- In the multiplayer online battle arena video game Dota 2, the hero Enigma conjures minions called Eidolons with his spell Demonic Conversion.
- Many Final Fantasy games, specifically Final Fantasy IX, Final Fantasy XIII, and Final Fantasy Type-0, allow players to summon magical entities called "Eidolons" to assist in battles.
- In the Pathfinder Roleplaying Game, an eidolon is a supernatural creature bonded to a character of the Summoner class.
- In Dungeons & Dragons, 4th Edition, an eidolon is a golem-like animated statue brought to life by a shard of divine energy.
- In Dungeons & Dragons Online, an eidolon is an animated shadow summoned by the Necklace of Mystic Eidolons.
- In Eclipse Phase, an eidolon is a specialized computer program that acts as digital body for digitalized minds, allowing infomorph characters to specialize.
- Eidolon, a 2014 first-person narrative introducing the protagonist or player-vehicle to a far-flung post-apocalyptic western Washington. The title was taken from Walt Whitman's poem "Eidolons".
- Aura Kingdom, an MMORPG produced by Aeria Games, has a plot-line that revolves around creatures called Eidolons.
- In the 2012 MMORPG Guild Wars 2 there is a shield with a ghostly appearance called Eidolon.
- In the Sid Meier's Civilization: Beyond Earth – Rising Tide an Eidolon is a Purity/Supremacy (aka Mastery) hybrid upgrade of a Soldier unit.
- The video game Warframe features an update entitled "Plains of Eidolon", which added an open-world prairie zone inhabited by nocturnal machines known as "Eidolons".
Film and television
- In the 2014 television series The Bridge, season 2, episode 10, "Eidolon".
- In the 2004 television miniseries "Farscape: The Peacekeeper Wars", there is an alien race known as the "Eidolons".
- Eidolon is an album by the German melodic black metal band Dark Fortress.
- The 8th track on Karnivool's album Asymmetry, the 5th track on Cities of the Plain's album Where Our Homes Used to Be and the 1st track on Epica's album The Holographic Principle are called Eidolon.
- The 7th track on The Decemberists' 2015 song, "The Wrong Year", contains the line: "Sing me some eidolon, and I'll sleep all the winter long."
- The 7th track on Allan Holdsworth's album The Sixteen Men of Tain.
- The 1st track on the Usnea album Portals into Futility is "Eidolons and the Increate"
- The 5th song on The Faceless' album Autotheism, named The Eidolon Reality
- The 7th track on The Mars Volta's 2012 album Noctourniquet, "In Absentia", contains the line: "Smokestack burning, Eidolon turning. I won't ever let you go".
- The 2nd album by the band Rishloo.
- The 10th track on Junius' album Reports from the Threshold of Death named "Eidolon and Perispirit".
- Holmberg, Ingrid E. (Spring 1995). "Euripides' Helen: Most Noble and Most Chaste". The American Journal of Philology. The Johns Hopkins University Press. 116 (1): 19–42. JSTOR 295501.
- Meltzer, Gary S. (Oct 1994). "'Where Is the Glory of Troy?' 'Kleos' in Euripides' 'Helen'". 13 (2). University of California Press: 234–255. JSTOR 25011015.
- Papi, Donatella Galeotti (1987). "Victors and Sufferers in Euripides' Helen". The American Journal of Philology. The Johns Hopkins University Press. 108 (1): 27–40. JSTOR 294912.
- Barasch, Moshe (2005). "The Departing Soul: The Long Life of a Medieval Creation". Artibus et Historiae. IRSA s.c. 26 (52): 13–28. JSTOR 20067095.
- Carpenter, Frederic I. (Mar 1942). "Walt Whitman's 'Eidolon'". College English. National Council of Teachers of English. 3 (6): 534–545. JSTOR 370944.
- Encyclopedic Theosophical Glossary: A Resource on Theosophy, G. de Purucker
- Morph Recognition Guide
- Kelton Sears (August 26, 2014). "Eidolon Asks Us to Imagine a World Without Us". Seattle Weekly. Retrieved December 13, 2016.