An impostor is an individual who takes on the persona of someone else, pretending to be that person. Usually the reasons for pretending to be someone else are fraudulent in nature, although there are times when people take on deceptive identities for perfectly legal reasons, such as law enforcement stings or cases where having a body double is used to provide security. The level of skill on the part of impostors varies, as does the underlying reason for taking on someone else's identity.
Some people live as impostors full time, dedicating their entire lives to pretending an identity they were not born to. These impostors can live under tremendous stress, as they may fear being revealed at any time. Full time impostors may pretend to be someone in order to have access to wealth or power; most famously, historically people have pretended to be members of royal families, sometimes taking on someone's identity and in other cases creating a new identity as a previously unknown relative. An impostor may also live part time in the assumed identity, just long enough to accomplish the desired goals.
Impostors can take on the identity of legal representatives like lawyers in order to trick people into admitting information, signing paperwork, or becoming involved in confidence tricks. When they pretend to be ordinary individuals, they can fraudulently impersonate bank customers to empty their accounts, and may engage in other activities like doing deals in someone else's name or committing crimes with an assumed identity. The impostor can use a variety of techniques including assuming an identity of someone who looks similar and mocking up identity documents to exploit the similarity, as well as wearing makeup and prostheses or even having surgery to look like someone else. An impostor may also pretend to have been at the site of a famous event like a battle or a historic incident, taking on a false identity without assuming someone else's.
In the law enforcement community, impostors may be used in criminal investigations to collect information. Taking the impostor as someone else, people let down their guard and may make deals or make revealing admissions that wouldn't happen in the presence of a stranger or a member of law enforcement. This can also be a security technique, with doubles being used to impersonate someone who is under threat to make it harder for that person to be attacked. Sometimes, people call on their doubles to make public appearances for them when they don't have the time, inclination, or energy to do so.
Impostors can know their subjects very well and may rely on tactics like avoiding close associates of their victims, using low light and crowded environments to make it harder for people to inspect them closely, and using well-known personal items like rings to further their impersonation. People are not always very observant, especially with people they do not know well, and some impostors can succeed despite not having a strong resemblance to the victim.