Have you ever read the book The Color Code by Taylor Hartman, Ph.D.? It is a great book about identifying your personality, and the personalities of those around you. It is a great way to learn about yourself and how to deal with others.
It is also a great characterization tool. I give each of my characters a core and secondary Color and - BAM - I instantly have their personality firmly on my mind. It only takes two words:
To me those two words invoke a complete picture of a person's behavior, drives and complexities.
Of course that is not the end. I go on to do more. But then when I am writing I keep falling back to my characters Color.
I highly recommend using The Color Code to help when building your characters. Or - if you have another favorite personality classification method - use it.
How about you? How do you define the personality of your characters?