In addition to McKee’s and Egri’s books, I have found one other book to be tremendously useful in creating believable, rich characters with strong motivations.
It’s the Diagnostic and Statistical Manual of Mental Disorders, currently in its fifth edition. Some call it the DSM for short. The fourth edition is more punchy and more direct, and a lot of diagnosticians prefer the old to the new; but for a writer’s purposes the version doesn’t matter.
Open up this thick book to a random page, and you have a complete and fascinating description of character traits for a random character. Let’s do that now: “Has deliberately engaged in fire setting with the intention of causing serious damage.” How cool is that! That’s a friggin’ one-hour crime drama right there, and the character is already mapped out for you on the page in loving detail.
Let’s go again. “Preoccupation with one or more perceived defects or flaws in physical appearance that are not observable or appear slight to others.” What, you can’t see my extra nose? You can take that character trait and run a hundred different directions with it.
Oh, one more, please! “Recurrent thoughts of death (not just fear of dying), recurrent suicidal ideation without a specific plan.” In a sentence or two, you’ve established a protagonist and given him a problem that needs solving. Neat, quick, and punchy.
The DSM works brilliantly as a rogues gallery, or as a source for richer and more complicated characters. The DSM gives us believable, immediate problems for our characters to solve.
You could write for ten lifetimes and still not run out of story ideas if the DSM were your only source for characters.
Thank you. Thank you, DSM 5. I love you.