Complete Monster/Fable

The Fable series is known for its heinous main antagonists
 * The first Fable had Jack of Blades as its main antagonist. Basically he leads a gang of bandits to wipe out your home village and kill your father, blinds your sister, who would later become a recurring character in the series, and in the end, murders your mother before the final battle. A mystical being from the underworld, he has no redeeming qualities whatsoever and acts in the most cruel and manipulative way possible.
 * Fable II had Lord Lucien, who shoots and kills your sister in the beginning while you were children, before shooting you out the tower's window. He then works the kingdom to death to build a magical spire that would grant him his dark wish to purify the land. While driven mad by his loss of his wife and daughter, he has no respect of the life of others, increasingly so as the game wears on. While he is a Well-Intentioned Extremist in the beginning, he starts clearly fitting the trope by the game's end through Motive Decay. He also will murder the hero's family if he or she has one, telling the hero about it cold fashion, even gleefully. And finally, he shoots your loyal dog.
 * Lucien's experiment the Commandant is a sadistic bastard. He introduces himself by stating he has broken 272 men beforehand, proud of this. He then makes sure Lucien's prisoners are starved and makes you kill your only friend there. It feels so satisfying to kill him after this, but this is ruined by the revelation that he is not the only one of his kind. Bonus monster points to Lucien for making this guy.
 * Reaver. In the second game he manages to double cross the main character at least twice, was revealed to be the person responsible for . In the third game he controls the Bowerstone industrial sector, which he forces children to work in factories and shoots workers who slow or grow tired, protest, or break some unannounced rule he has yet to think up. He also acts as an advisor to the king in which his suggestions will be something along the lines of deforestation and tearing down a school to make room for a whorehouse.
 * The Crawler from Fable III is pure death and destruction. If you don't need more convincing, when you first encounter it with Walter, . After it forces   it is revealed that it  . Then after it attacks Albion   and  . Most Eldritch Abomination kind of creatures would operate with Blue and Orange Morality and be exempt from this as a result. However, the Crawler takes glee in this (or at least its perception of morality is not properly explored) and qualifies.