Destroyer of Innocence

A Destroyer of Innocence is a type of villain who is responsible for a "loss of innocence". A "loss of innocence" occurs when a sympathetic and (usually) somewhat defenseless character is broken or harmed in some way or similar; this often invokes great feelings of anger by audiences and marks a common Moral Event Horizon. It can also refer to an event that causes unprecedented outrage in society, such as child murder and terrorist attacks, which challenges our concepts of what people can do to each other. Often, victims whose innocence are lost would never be the same person they used to be.

Destroyers of Innocence are villains who effectively "destroy" the innocence of a story, setting or character; they are often especially wicked beings who ruin lives and their crimes can never truly be reversed as it erases the concept of "innocence", though some rarer examples do not fully know that they are responsible for this occurring (e.g. Scar from Fullmetal Alchemist).

A Destroyer of Innocence is the evil opposite of a Protector of Innocence.

Examples of this type of villain are as follows:

1. Characters who abuse/corrupt a child or someone with a childlike mentality (many "Fagin" types fall into this category). Examples are Madara Uchiha, Ozai, Medusa Gorgon, Sebastian Shaw and Yakone.
2. Characters whom a protagonist has admired deeply in the past (even without their knowledge); upon finding out the character's true nature, the protagonist is visibly distressed. Examples of this are Charles Muntz from Up, Yokai from Big Hero 6, Ernesto de la Cruz from Coco, and Sōsuke Aizen from Bleach, who has shattered Momo Hinamori's trust in him by betraying the Gotei 13. 
3. Characters who betray loved ones, family, or friends, especially if their betrayal is extremely brutal and treacherous in nature. Good examples of this are Scar's betrayal of both Simba and Mufasa in The Lion King, Griffith's betrayal of Guts and Casca in Berserk, and Prince Hans' betrayal of Anna in Frozen.
4. Characters who mastermind a particularly shocking event, such as a terrorist attack or massacre of innocents, which in turn causes a deep and lasting "loss of innocence" in his or her setting. The event itself can also count if it has profoundly challenged people's perception of the world. An example of this type of villain would be Isaac Ray Peram Westcott from Date A Live, who caused the death of over millions of people in his wars and turned an entire city into a battlefield, killing hundreds of people, also as destroying an entire reality and killing his own daughter. Another good example was the Joker, whose scheme to destroy Gotham murdered Harvey Dent's fiancee and scarred half his body, turning him into the villainous Two-Face.
5. Characters who apparently seem to be harmless or even innocent, but it is only one facet to hide its nature and can easily commit atrocities. For example, Eric Cartman lost his innocence since he killed Scott Tenorman's parents in the South Park episode "Scott Tenorman Must Die".
6. Characters who turn their victim to the dark side, often developing the "Evil Vs. Evil" scenario where their victim seeks revenge on those who destroyed their innocence. Good example of this are Judge Hopkins and Count Bleck's Father.

Note: The desctruction of innocence doesn't neccessarily apply to children or teenagers being exploited, but also to regular adults or even mature heroes with relatively innocent mind and intentions who are forced to commit atrocities/participate in mind-breaking situations with murder/torture involved due to the actions or direct influence of the villain. 

See also

• Destroying the Innocent at the The Evil wiki, for further information about how villains destroy their victims' innocence.