An actor or actress is a person that performs in films, television, theater, radio, video games or even on the street. Traditionally, the term "actor" was restricted to men, and there were no actresses. When they did the term "actress" was used for women from the 17th century to about early 20th. In the ancient and medieval world, it was considered disgraceful for a woman to go on the stage, and this belief continued right up until the 17th century, when in Venice it was broken. In the time of William Shakespeare, women's roles were normally played by men or boys.

An actor has often his or her appearance changed: for example, by wearing make-up, a wig, and a costume. Specialized professions may be called on to help with this process.

An actor usually plays a fictional character . In the case of a true story (or a fictional story that involves a real person) he or she may play a real person (or a fictional version of the same), possibly him- or herself.

In the case where an adult actor is used to play a prepubescent boy this is sometimes a woman because in some regards a woman has a closer resemblance to a boy than a man: high voice, round shapes, little facial hair, size. However, notable differences include the breasts and the wide hips, and although on average smaller than a man, a woman is still much taller than a young boy.

An adult playing a child occurs more in theater than in film: film is supposed to be more realistic, and it is easier for a child to play separate film scenes than a whole play in one sequence.

Peter Pan was traditionally played by a woman, with the additional reason that a small woman was easier to lift on stage in the flying harness. The tradition of the principal boy[?] in pantomime may be compared.