Descriptions of the type, lifted or adapted from a variety of on-line sources (citations at bottom):
Personality Type One: The Reformer
Childhood Origin: Disconnected from father-figure.
Basic Fear: Of being corrupt/evil, defective
Basic Desire: To be right.
Healthy Sense of Self: I am reasonable.
Characteristic Vice: Self-righteous anger.
Characteristic Virtue: Wisdom.
Hidden Complaint: I am right most of the time, and it would be a better world
if people listened to what I tell them.
Key Defense Mechanisms: Repression, reaction formation, displacement.
May be objective, balanced and morally heroic, or repressive, critical and perfectionistic.
Healthy: Conscientious with strong personal convictions: they have an intense sense of right and wrong, personal religious or moral values. Wish to be rational, reasonable, self-disciplined, mature, moderate in all things. Extremely principled, always want to be fair, objective, and ethical: truth and justice primary values. Sense of responsibility, personal integrity, and of having a higher purpose often make them teachers and witnesses to the truth.
At Their Best: Become extraordinarily wise and discerning. By accepting what is, they become transcendentally realistic, knowing the best action to take in each moment. Humane, inspiring, and hopeful: the truth will be heard.
At the core of Enneagram style number One is a strong unconscious tendency to compare reality with what should be. Ones generally have a set of standards by which they evaluate themselves, the behavior of others, and the world around them.
Ones can be selfless and morally heroic, willing to sacrifice a great deal for principle. If they have a cause or mission, they might work hard and responsibly towards its fulfillment. Ethics and personal integrity are put above expediency, profit or easy solutions. An awakened One might display a balanced, cheerful perfectionism that is tempered by forgiveness and compassion.
Ones can become openly critical, angry when their reforming zeal isn't shared by the world at large. They might still work hard and hold themselves to strict standards of behavior but their speech could be punctuated by sharp-tongued remarks, as anger breaks through. Their calm, ethical perspective gives way to dualistic thinking - "either/or" propositions, right/wrong dilemmas that reduce complex situations down into black and white choices.
This type is sometimes called the perfectionist, but ones also have a strong sense of morality, responsibility, and justice that go beyond mere perfectionism. Average ones are driven by their "inner critic", an inner set of standards that tends to be quite rigorous, consistent, and independent of what other people might tell them. Average ones are often very critical of others, but they are even harder on themselves, ruthlessly excoriating their own failures to reach the highest standards in whatever they do. Ones get much of their energy from anger, and at best, this energy is channeled into discipline, organization, a strong work ethic and a love of fairness, justice, and truth.
They look at reality and see what is wrong. They sort for fault, for flaws, for what ought to be there and isn't. They walk around asking themselves, "What's wrong with this picture?" They have high standards to which reality must, but cannot, conform.
They turn the scolding light of faultfinding on themselves first. Often ones grew up in an atmosphere in which they were criticized, perhaps severely, and were told that criticism was done in the name of love. "If I didn't love you, I wouldn't correct you. I tell you what is wrong because I love you." Children turn all attention into love anyway, so they interpret criticism as an act of love.
So to be good to themselves, they criticize themselves.
With their intense moral concern and their interpretation of criticism as love, Ones do not want to be loved for their charm or beauty. They want to be appreciated and loved for the good work they do and their moral fiber. Love comes after evaluation, it is not be given for charm without effort.
Ones are polarized against their own sensuality because sensuality can easily lead to moral deviance. Passion, impulse, bliss -- these threaten the moral order.
Ones get healthy when they get funny. They need to treat themselves to some humor.
Sources:
http://www.enneagramcentral.com/
http://www.enneagramspectrum.com/styles/default.htm
http://www.enneagraminstitute.com/home.asp
http://www.9points.com/
http://michaelgoldberg.net/home.htm