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.
The concept of the eidola of the dead was explored in various literature regarding Penelope, who in later works was constantly laboring against the eidola of Clytamnestra and later Helen herself.
Homer's use of eidola also extends to the Odyssey where, after the death of the suitors, Theoclymenos notes that he sees the doorway of the court filled with them.
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 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 an Eidolon.
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 "Into Everywhere", a sci-fi novel by Paul McAuley (2016), Eidolons play a central role and often "inhabit" the minds & bodies of people. These Eidolons are thought to have been left behind by an "Elder Culture".
In the original Tomb Raider game from 1996, the main character Lara Croft encounters an eidolon of herself, created by her antagonist Jacqueline Natla. The eidolon mirrors the player's in-game movements directly. It re-appears in the 2008 sequel Tomb Raider: Underworld.
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".
Eidolon, the higher self in the tabletop Roleplay game Wraith: The Oblivion Less prominent and less conscious than the Shadow Self; which is played by another game member. The higher self can be drawn upon in times of awareness and need; the opposite to the shadow self that strives to take the character into oblivion (eventually becoming the prominent personality and turning wraith into a Spectre).
Eidolon is an enemy encountered in Hexen II, the oldest and most powerful of the Serpent Riders, and the main antagonist of the game.
Film and television
In the 2014 television series The Bridge, season 2, episode 10, is titled "Eidolon".
In the 2004 television miniseries "Farscape: The Peacekeeper Wars", there is an alien race known as the Eidolons.