When you were born you were given a family name, an identity.  If you end up in prison, you lose that name and your identity becomes a number. When you travel to other countries, you must have a passport which tells the immigration agent where you are from.  Certain jobs give you new identities by which people would identify you.  For instance, officer so and so, Doctor…x, NCIS, NYPD, ect. They are not just known by their names, but also by what they do.