Complete Monster

"I met him fifteen years ago. I was told there was nothing left. No reason, no conscience, no understanding; even the most rudimentary sense of life or death, good or evil, right or wrong."

—Dr. Loomis, Halloween

The Complete Monster is the most depraved of all characters; a villain utterly lacking in redeeming features. Trying to put a value on the evilness of a Complete Monster is like calculating the credit score of Bill Gates: it's a moot point.

Or, anyway, that is how the character is presented in the story. The character is a bad guy, full stop. The author has not taken the character through any actions toward redemption, or at least any that stuck.

The Complete Monster can be recognized by these signs:

Atrocious acts: the character is truly heinous by the standards of the story, and has crossed the Moral Event Horizon, usually several times to empathize of how evil they are. Villains who only cross the MEH once usually does not qualify, although rare examples exist if the line they cross was heinous enough for the standards of the story.
Moral Agency: the character can distinguish right from wrong but choose to do what is wrong and stay evil all the time. For this reason, forces of evil such as eldritch abominations, demons or artificial intelligences usually do not qualify unless their Moral Agency is made clear.
Seriousness: the character's terribleness is played seriously, even if the work is light or comedic. Other characters in-story must express genuine fear, hate, and revulsion of this character.
No love nor compassion for anyone: the character can never feel love for others, only for themselves. If complete monsters claim to "feel love", that love would merely be obsession or perversion.
No sympathy: the character has either no Freudian Excuse to validate their crimes, or their Freudian Excuse is presented in-story as inadequate. Any sympathy evoked in their backstories is long gone in the present.
No redeeming quality: they are completely devoid of altruistic qualities, show no regret for their crimes, are never redeemed or have any possibility of redemption.
No honor: in other words, a complete aversion of Even Evil Has Standards. They have no standards whatsoever.

Please note that a character crossing the Moral Event Horizon does not alone make them a Complete Monster. This trope isn't just about what the character does, but about what the character is. Their monstrous characters are reflected in their heinous deeds, which is what puts them a cut above the regular villains. And whatever their position, a Complete Monster has to go the full mile and meet all criteria: they are the worst they can possibly be in their role, in the space and scale they occupy.

Offscreen Villainy is advised against, with few exceptions depending on how clear the results of said villainy are.

Tropes Are Not Good; the Complete Monster can sometimes be indicative of lazy writing. A villain with no redeeming qualities can be viewed as exceedingly simplistic.

This trope is not Gushing About Villains You Like. A recurring evil character either has redeeming qualities presented as such within the moral framework of the story, or they don't. The Complete Monster may be a Magnificent Bastard or a Draco in Leather Pants to some audience members, but the completeness of their monstrosity does not depend on how well the audience receives them.

No real life examples, please; calling other people completely irredeemable is rude at best. Calling yourself one implies either a lack of understanding of the trope or severe mental illness.

The following works are especially notable for featuring Complete Monsters.

This trope is ubiquitous; examples playing it straight need not apply.