User blog comment:Ngh93/What REALLY makes a villain a Complete Monster?/@comment-27818776-20150326235216

A complete monster is, by definition, beyond the moral event horizon. They are beings of pure evil. This is how you can tell when you have a CM on your hands:

They are the most heinous individuals in their settings. They must also be generally heinous. An evil overlord wouldn't usually be a CM, unless they do something that crosses the line like torturing their citizens or committing mass genocides.

They must not have redeeming qualities.

They can never feel remorse for their actions.

They don't have tragic backstories.

Usually speaking, a single MEH doesn't make the villain in question automatically evil; it just means that they're irredeemable at that point. This depends on how bad the MEH is in some cases.

CMs must also be defined by their character.