Many mystery writers enjoy putting real-life people into their stories so they can torture and kill them. Ex-spouses are a favorite target, as are hateful former bosses. The authors who go after them tell their audiences gleefully how much zest that adds to the writing process, and how much more lively it makes their books.
So, early on in my writing career, I decided to give it a try. Why not? I could think of two people I've known who seemed irremediably despicable, and I thought one of them might fit into the story I was then working on. He was lazy, mean-spirited, insincere, a bully and a liar. I figured he'd earned a little fictional what-for.
But then an odd thing happened. My story development ground to a halt, and - very unusual for me - I found myself trying to avoid writing. It was clearly on this character's account. He was sucking all the life out of my story, trying to push the plot in a direction favorable to him, never mind what the story wanted or needed. Very shortly, I decided this approach was not going to work for me. "Get out of my book, jerk," I barked. "You've pissed me off enough in the real world; I must have been crazy to let you into my book." So out he went, and the story promptly resumed its proper flow. My relationship with this guy had been close enough and sufficiently longstanding that his bad qualities had overwhelmed my capacity to see - or imagine - any other side of him.
It works better for me to start with people I don't know well, and about whom I have mixed feelings. That allows the characters to grow into rounded human beings, rather than stereotypes or comic-strip personas. Dr. Colin Sanford, in A Perilous Conception, is the result of such a process. His prototype was the most breathtaking example of a doctor who thought he was God I've ever encountered. Not an admirable trait, but over the years, since I wasn't close to him personally, I could watch him go through god-awful contortions to maintain his distorted self-image and overblown self-regard, and feel some sympathy for him. I was able to be an interested observer, trying to figure out just what did make Sammy run. And that gave Dr. Sanford plenty of space to develop into his own person. In the end, the only attributes that remained of his prototype were the monster ego and short stature.
Dr. Sanford's prototype has been dead a good while now, and you know what? I miss the crazy bastard. I'm not at all sure he's inspired his last character in one of my books.