This question intrigued me, as many intriguing questions do, and has been something mulling around in my head ever since.
Having spent time in a drama class, and having known many people who have continued with "drama", there are a few personality traits that seem to stem from these types of people. Most are very humanities oriented, choosing to focus on the grey areas instead of the black and white in the science/maths departments. Most have incredible amounts of energy and, at times, can be hard to keep up with. Many of them are thinkers and observers, as well. They generally have a higher grasp on how other people act with each other. Almost all are very confident and comfortable with themselves. This is a generalisation, but it seems to be how "actors" act off stage. They obviously act as "themselves". But who are they?
Actors, when preparing for a role, have to put vast amounts of thought in to many different aspects of a character. Physical aspects, such as their walk, their mannerisms and the way they talk have to be construed, constructed, and practiced to the point where the actor can throw away their personality in exchange for a new one. They have to file away their personality so as to let the character come alive and be believed. Actors must know the stories, the past of their characters. The characters dreams, quirks and interests all have to be explored.
The role of an actor is to essentially abandon who they are so as to become someone else.
How do actors actually create these characters though? They have to be based upon something. Writers must draw upon their own knowledge bank and personality to be able to write about something that is completely different. So too, must actors. To convey sadness to the audience the actor must know what sadness is like and how it feels. So if actors constantly abandon "who they are" for completely different characters and base many of their characters on their own experiences it begs a different set of questions...
Who are actors? Are all their characters a mixture of their actor's experience, or are actors merely a mixture of all the different characters they have played?
It could almost be seen in either of those two ways.
I think in a lot of ways it is harder for actors to determine who they actually are, which seems to run contrary to the personality traits they display. Many of the better "actors" that I know have very distinct character traits that stand out and can easily be described. Which raises another question. Are those who are good at acting naturally outgoing and unique? Or do they exaggerate their character traits as perhaps a (conscious or subconscious) reflection of the difficulty they may have in knowing who they are?
So I didn't really go anywhere on this, but hopefully it gave you some food for thought. I am interested to hear people's thoughts on this subject.
"Robert Cohen says, 'all people, and all characters in plays, think about their situation more than about their own personality or character.' This is almost always true about people, and is certainly the way actors should think during a performance. But actors, off the stage, must think about their own personality and character. If you do not know who you are, if your instrument is not limber and under your control for the most part, you will never be a great actor. Master actors cultivate effortless and automatic control of their instruments"