There are many traits of an actor or actress but I would narrow it down to the three main traits one should have as a performer. First off let me start out by saying that actor in the Greek language is one who interprets but in this sense it is one who interprets a dramatic character.
The actor acts in dramatic performances and productions. They are involved in screen and off Broadway plays, theater, film, television, and even radio. Acting is said to derive around 534 BC.
The first known person to get on stage and recite words intended to be someone other than themselves is Thespis. He performed at the theater Dionysus. Thespis told his narratives in song, third person narrative, and dance. You may have heard of actors being called Thespians and this is mainly because of Thespis.
Unlike in present time were we placed our actors on high pedestals back in the early middle ages actors were not known as a high status. People tended not to put much trust into the traveling actor. But now people have come to almost worship and even being obsessed over actors.
One of the traits an actor must have is technique and discipline. You must learn the ways of the art. You should be well acquainted with different acting styles. There is method acting, representational and representational acting, and acting as an opposite gender.
You should learn the history to get to know the essence of the art. The second trait you should have is creativity and freedom to express yourself. You must be willing to make a fool of yourself for the art. You have to be able to learn how to let go and be as free as a child while still maintaining that constant control of your craft.
The third technique to possess is the passion and the energy that brings. When you love something and love to do it that in turn comes across in your performance. The feeling that an actor brings to the table is that of real raw sincere emotion and the if you can find your passion for the piece and character you are portraying then you would make a phenomenal performance as an actor.
Learn how to find that inner energy that you need to bring from the inside to the surface of the character. As an actor you should always try to find common ground between you and the character so that your presence is felt as one and not as you playing the part but being the part.