When I'm writing a character into a story, it could probably be sorted into any number of groups. One of the most obvious to me while I'm writing is whether or not I can see the person's face. Sometimes, when I adapt a character from someone I once knew, it's easy. I do see the face, the hair, the walk.
The editor in Death of The Limping Man is based on the publisher of a newspaper I worked for in ages past. He was a remarkable man, and to borrow a few of his personal characteristics for the character in the novel is pretty cheeky, but I wanted to do it: it's a little tribute. That man -- a true gentleman -- taught me a lot about deadlines, writing. the tyranny of column inches, and bravery. He wore an eye patch and I can still see him today.
In the book, the editor employs Notepad MacDonald, a young woman reporter. I created her from whole cloth, and it took me a while to see her face. The funny thing was, I could see her right away in profile, in a kind of 1940s studio photographer head shot -- heavy shadow and lots of back light. It took time to start to see what was important in her face: the intelligence, humour, independence, optimism, and loneliness.
Notepad meets Mrs Evans, an old lady who wears a hairpiece. Not a wig, mind you, just a sort of bun. A woman I once knew had bought such a bun -- she would wrap her hair around it for a quick tidy up. It looked okay: it matched the brown of her hair, but as she got older, her brown hair aged into grey. The hairpiece did not. She never noticed -- and that said it all about how she saw herself. I used it when creating the irrepressible Mrs Evans -- a character who, like the editor, may appear in further stories.
I think that principal characters in a book should grow with the story. The supporting players are seen less and need to be quickly defined for the reader -- because they might or might not be back. If they do come back, it's not often for long. But it is important that principal characters grow and change and maybe it's not such a problem that I don't see them very well at first.