When I decided that the characters in the story would span a number of books, I thought about where to start them and how to handle their development. The physical presence of a character may not change too much over months, but it will over years. The same is not necessarily true of personality. There may be something there, lurking, that we don't see at first meeting.
The character of Constable Hoegy was born part-way through the writing. I could see I needed a foot-soldier on the team. After all, they do a lot of the necessary questioning, taking of statements, fetching of witnesses, opening doors, driving cars, and so on. I had written an unnamed constable at the crime scene, and I went back to Chapter 1 and gave him a name. Constable Hoegy.
What was he to be like? I decided he'd be young, fresh to the force, just finished his training. He could grow and develop that way -- a character arc that would last over any number of books. Each book would reveal something new, giving readers fresh perspectives and maybe a surprise or two.
Some years ago, I was directing a production of Rosencrantz and Guildenstern Are Dead, the great Tom Stoppard comedy. A few days into rehearsal, an actor had to withdraw. I needed an Horatio. A friend came to my rescue, and brought along a young actor she had only just met, but really liked. The young man was tall and dark-haired -- a perfect foil for my young, tall, blond Hamlet. I asked him to read some lines and hired him on the spot.
Around me, this young actor was always a little nervous and very quiet. But his big cow eyes darted with mischief. If only I had known what terrors this presaged, I still would have hired him. Constable Hoegy began to take shape for me: intelligent, eager to learn, hard-working, and incorrigibly wayward. Stay tuned.