A doppelgänger is the ghostly - in some cases, the physical - double of a living person. The word "doppelgänger" originates from German and is derived from Doppel (double) and Ganger (goer).
In most mythology, the doppelgänger is often referred to as an "evil twin". It is an exact replica of a specific human being.
When one sees their own doppelgänger it is said to be an omen of death, or a warning of approaching danger. A doppelgänger seen by a person's friends or relatives may sometimes bring bad luck, or indicate an approaching health problem.