Ok, in the first instance, they are an amalgum of people I’ve met or seen before, but they always seem to have what might be called an avatar in the back of my mind.
So, as a case in point, some years ago I was writing a story, but I didn’t have a clear picture of what my character looked like. I knew most everything else, but it made it difficult to go beyond a certain point.
Then I saw Bruce Willis in the original Die Hard, and the character suddenly took form in my mind. Of course, Bruce Willis wouldn’t recognize that my character was based on him, but if the film of the book was ever made, back then, he would have been ideal cast as the main protagonist.
In another instance, I was writing a YA story for my granddaughter and after she read the first 10 chapters I asked her what she thought. It was a good story, but the characters needed another dimension.
We then sat down and discussed who we might ask to play roles if we were casting a movie version.
It was unanimous, Lily James was Marigold. Probably not now, but when we first saw her. Emma Thompson was the Queen, and Jeremy Irons the King. We had others for the captain of the guards, the good witch, and the bad witch.
Sometimes it takes a casting call to picture how your character might take physical form, and if the actors selected are very versatile there are so many traits you can pick up.
The question is, do you cast your characters?