According to psychologist Carl Jung, humans have an
innate tendency to use a particular set of symbols to
understand the world.

He refers to these symbols as archetypes.

We are “hardwired” with archetypes.

Each archetype can be thought of as having a general
form that will vary only slightly from culture to culture
and from ere to era.

The Shadow is one of the most important and
ubiquitous of the archetypes, it can be thought of
as our "dark side".  It consists of those parts of our
being that are instinctual, rejected and pushed to
the unconscious. Examples include resentments,
obsessions and shameful memories, and emotions
such as envy, jealousy, depression and rage.

The Shadow is often projected out onto others, whom
we then view with disdain.

It is often the goal of Jungian analysis to increase our
awareness of the Shadow, acknowledge it as part of
ourselves, draw on its energy, and integrate it into a
psyche that is more balanced and whole, one that is
more aware and less conflicted - all this, without
acting out the Shadow's darker impulses.

Finally, the Shadow is often personified, and then
incorporated into our dreams, literature, and media.

Examples of the Shadow in media include:
Darth Vader of Star Wars, Mr. Hyde of Stevenson's
Dr Jekyll and Mr. Hyde, and Lord Voldemort of
JK Rowling's Harry Potter series.