Dark Priests or Dark Priestesses are popular villains; despite the names they are not required to be actual priests, as religious members of a clergy or Cult are applicable.

They use their positions to knowingly commit crimes at odds with their religions but convince themselves and/or others they are good or do not care. What makes them dangerous is that despite their obvious evils they can still hold power and due to their status as Men/Women of the Cloth they are hard to counter without backlash, especially when clergy members have greater control in a setting. In real-world religions, especially Christianity they are known as false preachers, false teachers and false prophets.

Alternatively they may not actually be part of a Clergy but deranged and/or evil beings adopting the guise of a cleric or corrupt and dishonorable clergy Members who renounce divine allegiances to worship otherwise and/or commit crimes.