Jean Piaget was a Swiss psychologist who developed a theory of moral development with four distinct stages: (1) Anomy from birth to age 5 where children do not distinguish right from wrong, (2) Heteronomy-Authority from ages 5-8 where children obey rules out of respect for authority, (3) Heteronomy-Reciprocity from ages 9-13 where children follow rules of fair exchange and reciprocity, and (4) Autonomy from ages 13-18 where children think more critically and take others' perspectives. Piaget believed moral judgment develops from children's own observations rather than direct teaching from adults.