Heretic is a game released on a modified version of the Idtech 1 engine, taking heavy inspiration from it's predecessor, DOOM.

Not much is known about the Seven Nations other than the fact that it contained the race of the Sidhe Elves, a mystical race who defended the Tomes of Power and sacred candle flames that burned eternally to represent the seven armies of the nation.

The Sidhe believed in a certain prophesy speaking of a catastrophe, which was proved true when the three Serpent Riders came along.

D'sparil was a part of a trinity of three Serpent Riders, extremely powerful sorcerers that showed their power to bring the war of the Eastern Provinces to a screeching halt. This display of power had made the people of the Seven Nations start worshipping them, naming themselves the Order of the Sign. As they begun to worship the Serpent Riders more and more, their free will and spirit were feasted upon.

Players in Heretic take control of an unamed Sidhe character, who along with the rest of his species, rebelled against D'sparil and his minions after realizing the prophecy having come true. Due to their defiance the entire race were deemed heretics by all other nations and were nearly brought to extinction by the power D'sparil's armies.

The few that remained from his reign of terror hid themselves away to avoid the massacre, except for the player (later to be named Corvus in Heretic II), who equipped a mystical elven wand passed down by his ancestors and begun a conquest to defeat D'sparil, eventually killing the Youngest Serpent Rider alongside all that worshipped him.

D'sparil had placed a curse upon the player sending them into another dimension he had previously conquered, which then kicks off the plot for Heretic II.

Heretic added many new features to the Idtech 1 engine such as moving floors, an inventory system, a flight system, translucent and pushable objects, etc.