Type One, named the Reformer or Perfectionist in the Riso-Hudson nomenclature, is placed in the body or gut triad with Eight and Nine, and its core emotional material is therefore anger. The system gives it a basic desire to be good and to have integrity, and a basic fear of being corrupt, defective or wrong. Its passion, in the vocabulary Oscar Ichazo took from the Christian capital vices, is anger, and its corresponding virtue is serenity; the characteristic form the anger takes is resentment held in rather than expressed, since expressing it would itself be a failure of standards. Its wings are Nine and Two. Under stress the system places One at Four, taking on melancholy and a sense of being uniquely flawed; in growth it moves to Seven, becoming more spontaneous and less driven.
Riso and Hudson's second classification, the Hornevian groups drawn from Karen Horney's three neurotic trends and set out in The Wisdom of the Enneagram (1999), places One among the compliant types, alongside Two and Six, since the type's orientation is toward an internalized standard of duty and correctness rather than toward assertion or withdrawal. This is a separate axis from the body triad above; each of the nine types belongs to one of three triads by core emotion and to one of three Hornevian groups by interpersonal strategy, and the two groupings do not coincide.