An actor or actress is a person who acts, or plays a role, in a dramatic production. The term commonly refers to someone working in movies, television, live theatre, or radio, and can occasionally denote a street entertainer. Besides playing dramatic roles, actors may also sing or work only on radio or as a voice artist.

An actor usually plays a fictional character. In the case of a true story an actor may play a real person.
Acting is the work of an actor or actress, which is a person in theatre, television, film, or any other storytelling medium who tells the story by portraying a character and, usually, speaking or singing the written text or play.

A performance, in performing arts, generally comprises an event in which one group of people (the performer or performers) behave in a particular way for another group of people. Sometimes the dividing line between performer and the audience may become blurred, as in the example of "participatory theatre" where audience members might get involved in the production.

From the Latin word agere meaning "to do", this is precisely what acting is. In acting, an actor suppresses or augments aspects of their personality in order to reveal the actions and motivations of the character for particular moments in time. The actor is said to be "assuming the role" of another, usually for the benefit of an audience, but also because it can bring one a sense of artistic satisfaction. The first actor is believed to be Thespis of Icaria, a man of ancient Greece. He supposedly was the first to break away from the traditional singing chorus of the time, literally stepping away from the chorus and speaking to them as a separate character in the story. This may only be a legend, but in his honor a word was crafted: thespian, meaning any sort of performer but chiefly an actor. The International Thespian Society, a society comparable to a fraternity for students involved in the arts has also been named in his honor.

Actors are generally expected to possess a number of skills, including good vocal projection, clarity of speech, physical expressiveness, a good sense of perspective, emotional availability, a well developed imagination, the ability to analyze and understand dramatic text, and the ability to emulate or generate emotional and physical conditions. Well-rounded actors are often also skilled in singing, dancing, emotional expressiveness, imitating dialects and accents, improvisation, observation and emulation, mime, stage combat, and performing classical texts such as Shakespeare. Many actors train at length in special programs or colleges to develop these skills, which have a wide range of different artistic philosophies and processes. Modern pioneers in the area of acting have included Mani Madhava Chakyar, Konstantin Stanislavski, Jerzy Grotowski, Lee Strasberg, Uta Hagen, Stella Adler, Michael Chekhov, Viola Spolin, Sanford Meisner, Bertolt Brecht, and Maria Ouspenskaya.