The Enneagram personality type system

Fun Joel wrote a series of posts about a personality type system called Enneagram that he uses to help him develop characters. Here are the links to his posts:

Fun Joel The Enneagram (Part 1 - Intro)
Fun Joel The Enneagram (Part 2 - Complexities)
Fun Joel The Enneagram (Part 3 - How to Use It)
Fun Joel The Enneagram (Part 4 - How to Use It, cont'd)
Fun Joel The Enneagram (Part 5 - Subtypes)