Heretic is a dark fantasy first-person shooter video game. It was developed by Raven Software and published by id Software. Three brothers D'Sparil, Korax, and Eidolon, known as the Serpent Riders, have used their powerful magic to possess seven kings of Parthoris into mindless puppets and corrupt their armies.

The Sidhe elves resist the Serpent Riders' magic. The Serpent Riders thus declared the Sidhe as heretics and waged war against them. The Sidhe are forced to take a drastic measure to sever the natural power of the kings destroying them and their armies, but at the cost of weakening the elves' power, giving the Serpent riders an advantage to slay the elders. While the Sidhe retreat, one elf sets off on a quest of vengeance against the weakest of the three Serpent Riders, D'Sparil. He travels through the "City of the Damned", the ruined capital of the Sidhe, then past Hell's Maw and finally the Dome of D'Sparil.

The player must first fight through the undead hordes infesting the location where the elders performed their ritual. At its end is the gateway to Hell's Maw, guarded by the Iron Liches. After defeating them, the player must seal the portal and so prevent further infestation, but after he enters the portal guarded by the Maulotaurs, he finds himself inside D'Sparil's dome. After killing D'Sparil, Corvus ends up on a perilous journey with little hope of returning home.