An impostor or imposter is a person who pretends to be somebody else, often
to try to gain financial or social advantages through social engineering,
but just as often for purposes of espionage or law enforcement.

Pretenders for various thrones used to be common. Numerous men claimed they
were Dauphin, the heir to the French throne who disappeared during the
French Revolution, and there were three false Dimitris who were serious
pretenders for the throne of Russia.

Very daring impostors may pretend to be someone else who really exists,
although fast news media has made this rather difficult. Usually they just
misrepresent their financial status, educational status, social status,
family background or in some cases, their gender. Impostors are usually
aware of not being who they say they are, however there are borderline cases
who may have ended up believing their own tall tales. People may make false
claims about their past or background without being full-blown impostors;
non-existent military service seems common.

Many temporary impostors are criminals who maintain the façade for a time of
a caper to defraud their victims (like Wilhelm Voigt).

Others, like US prankster Joey Skaggs, do it as a prank or to make a point
of some kind. The latter usually reveal the truth sooner or later. Some,
like John Howard Griffin, have adopted other identity for purposes of
research, investigation or experiment. Note that although impostors usually
misrepresent their background, their intentions may not be criminal as such.
They may wish to start anew with a new identity or "go native"; i.e. adopt
identity and customs of other people.

Sometimes women have masqueraded as men to obtain privileges only men can
have or work in male-dominated professions. Some of them have fought as men
at least in Napoleonic Wars and American Civil War. Sometimes, an
organization or individual who has been fooled keeps quiet to avoid the
embarrassment and therefore allows the impostor try the same thing
elsewhere.

Of course, the most successful impostors are those whose duplicity is never
revealed so that we know nothing about them.