I carry strong visuals in my head of a heroic concept, which has developed and changed over time, but has defined most of the major characters in my books and stories. I also have a concept of the antithesis of this hero, whom I call upon when my storyline needs a villain. The "hero" has both masculine and feminine counterparts.
Sometimes, in books I have read, individuals I have known, and characters enacted in films and on TV, I see parts of this concept being played out. So, over time, I have built a repertoire of "actors" whom I can pull up to use in my stories.They say that actors look within themselves to find the parts of them that most resemble the characters they play, and I think that is true for writers as well.
Our concepts of heroic and anti-heroic behavior come from our own knowledge and perspectives. Even our villains come from projections of our own shadow aspects, which we choose to deny. (And so, when we see them in others, we become offended by those behaviors.)
Every man has an image inside his head of the woman he might have been if he had been born that gender. Carl Jung calls it his anima, or soul image. In the same way, every woman has her animus. These parts of ourselves also play a role in the characters that we develop.
So, yes, I believe, our characters are often treated like actors, but at bottom, I think, the actors are all us.