Someone who acts; someone who enacts a role;
In the most basic sense, an actor is someone who does something,
usually but not necessarily consciously and intentionally so, while in the
most figurative sense, an actor is a person who, possibly
professionally, plays roles in staged plays.
In either sense, there are some unclarities and ambiguities, but the basic
referents are clear, namely respectively to someone who does things he knows
or may know he is doing, and to someone who pretends to be someone he is not
in order to amuse or instruct people, possibly for pay.
The most interesting sense of actor is the middle one, namely when
it is used to refer to persons playing ordinary social roles, which is an
activity that has much more to do with playing on a stage than most people
Much of ordinary human social behavior can only be explained truthfully
when taking into account that this is to a large extent normally staged for a
public, who are outsiders to a group, in which persons play roles that involve
considerable amounts of deception, usually for the purpose of saving face, or
for taking advantage of the public.
The main reason the idea of actor is required to explain
ordinary human behavior is that much of
that behavior is make-belief, pretension, and intended to deceive, for all
manner of reasons, including moral ones such as trying to safe face, being
kind or polite to others, or behaving morally in one's group.