|“||Stare too long into the abyss and the abyss stares back.||„|
|~ Friedrich Nietzsche|
Darkness is usually the symbol of evil. Often, it is classified as a type of energy that the villain draws upon. In many good vs. evil stories, light is the good, the antithesis of the evil darkness.
Examples of Darkness as a symbol of evil comes from the fact it is used in many villains names, the "Prince of Darkness" (sometimes called "King of Darkness") is also a fairly common alternative name for The Devil himself - also in many fantasy settings the word "Dark" is suggestive of an evil-version of a species of faction that is normal good (or even a more malignant type of an already evil species/faction) - examples of this are the Dark Elves (from many different settings) and Dark Eldar (from Warhammer 40K).
In many religions and philosophies, darkness is seen as one of the most ancient forces, predating almost all things and in many ways, being related to the Greek concept of chaos (an empty void that existed before the "ordered" universe) - this darkness is not always seen as evil but it can be seen as negative, especially in the fact it represents either an abscence of life or order - both of which are seen by many as unwanted states of existence.
Darkness can also be represented as a sentient - or at the least intelligent - force in itself, whenever this is applied it is almost always evil. Examples of darkness being seen as sentient or somehow "alive" can be seen in the villain type known as the Dark Form or Dark Lord, depending on the writer.
Darkness is also used to classify a work of fiction as containing mature and often depressing and/or disturbing content such as death and suffering - it can also be used to refer to a personality-type that is prone to more negative thoughts or actions, such as a fixation on death or suffering: some subcultures (especially Goths and Emos) deliberately idolise this personality-type and may dress in black and listen to music that deals with angst or death as part of their identity.