Eidolon

Eidolon is the oldest and most powerful of the Serpent Rider demons from the Heretic/Hexen games. Eidolon makes his first appearance in Hexen's epilogue, moving a Korax's figure on a chessboard. He is the final boss in Hexen II. Eidolon has conquered the world of Thyrion and has appointed control over Thyrion's four continents to his dark generals, the Four Horsemen of the Apocalypse. The player must battle all Four Horsemen (along with all of Eidolon's lesser minions) before Eidolon himself can be confronted.

Eidolon's appearance is that of a red demon-type creature with goat legs. Although initially slightly larger than adult human when the player first meets him, he is very powerful, able to hurl three blue orbs of explosive dark magic power at you. After being damaged sufficiently, Eidolon appears to die, but this is merely a ruse. It is then that Ediolon reveals his true form, that of Larkyxamus, and produces a mysterious artifact. Eidolon draws his power from an artifact called the Chaos Sphere, a glowing blue orb that materializes during the fight. Eidolon uses the power of the Chaos Sphere to heal himself and also grows much larger by means of the Sphere's power. At this point, he gains several new attacks, which include the ability to hurl fireballs at the player, and even call down meteorite particles from the sky. Eidolon's strongest attack is to project a devastating stream of flame at the player. From the point where Eidolon is first healed and grew until the Chaos Sphere is destroyed, Eidolon is effectively invincible, as he uses the Sphere to heal himself after taking enough damage from the player. When the Sphere is destroyed, Eidolon is no longer able to heal himself and is defeated when the player lands the fatal blow. Eidolon's body bursts apart in an explosion of gore and brilliant light, and Thyrion is freed from his control.

Eidolon also created a female demon as a side project. The player has the ability to play as the Demoness in the Portals of Praevus expansion pack for Hexen II.