I have been asked that question or related ones several times in interviews and it always gives me pause. I really, truly, haven't a clue. My characters simply appear in my head and tell me their story. Perhaps I have undiagnosed schizophrenia?
Sometimes, as a story unveils, I begin to see specks of people I have known, composites if you will, of persons from my past. Most often not.
As a writer, I am constantly aware of my surroundings and the people in it. The least thing to catch my eye could be a catalyst for a new story.I guess it has more to do with perception for me. Is the man who stops to assist the lady with a flat tire on a backcountry road a good Samaritan or a serial killer? Can romance blossum when a honest returns a purse left in a Wal-Mart shopping cart? Can love turn the stone heart of a demon and earn him not only his soul but his soul mate?
Where do you think heroes come from?