Characters are like models of human personalities. They have to be complicated, tortured, loving, irascible, generous, and nasty. No one likes a goody goody hero, or a villain who is evil for the heck of it. When you are inventing characters, look for the thing that doesn't fit--the scar on the neck of an otherwise flawless woman, the hoarding impulse of the billionaire, the artificial toe of the runner. Make sure that their flaw runs their life to some degree, because this is what makes people interesting.
The art of good character creation is