One of my fascinations is family. Blood family and chosen family. Parent/child relationships, mother/daughter, father/son. Cousins. Aunts, uncles, and especially siblings. I like studying the way people shape one another.
My horse Markus (top) and his father, Fruhling (bottom)
When a character is forming in my mind, I ask myself what sort of parents he or she had. Was it a loving home? A happy childhood? Has the character made a conscious effort to be different from his parents? Is he unconsciously falling into the same bad habits and patterns as his parents? What about siblings? How many, and were they close? Did they fight constantly?
While characters are, for sure, possessed of individual traits and thought processes, their childhoods play a part in forming their outlooks on life. Troubled childhoods can galvanize characters. Happy ones can ill-prepare them for the evils of the world. There is such opportunity to create unique origin stories for our heroes. Even if I never mention it within the narrative of the story, I create a childhood and a family history for each character. It's a way to make them more real for me, so that I can then portray them realistically to the reader.