An eretik is a Russian vampire. In Russian stories, the vampire is associated with witches and sorcerers, which has been tied to the concept of heresy.
Heresy is the deviation on matters essential to orthodox faith. The idea revolved around the idea that the body would not decay normally if death occurred when the individual was outside the communion of the church, whether in an excommunicated state due to immoral behavior or due to heresy. The heretic may become a vampire after death.
In some stories, the emergence of the eretik vampire occurred upon the death of a person who had died without confessing his sins, thus seen as though the person had died in sin. Many of these people did not believe in God, and were seen as serving the devil as sorcerers.
The most common heretics that turned into vampires after death included practitioners of magic- kudesnik, porcelnik, koldun, or snaxar.
The vampire eretik possessed an evil eye that could draw a person caught in the vampire’s gaze into the grave.
Generally, eretiks were destroyed using an aspen stake driven into the back of the vampire or by fire.