Lawrence Kohlberg (1927-1987) was an influential US psychologist who is most recognized for the stages of moral development which identify the development of moral reasoning and ethical behavior in humans.
Kohlberg based his research on the work of Piaget and built upon it to develop his own theories.
Kohlberg based his Stages of Moral Development on his belief that moral judgment progresses with age and is primarily concerned with justice. Kohlberg divided his six stages of ethical behavior into 3 stages which are related to age and maturity: pre-conventional, conventional and post-conventional.
These three are then subdivided into two other stages that describe the moral rationales for the adoption of ethical behaviors. These stages are based on the premise that mastering the lower stages of moral development is essential for aspiring to the higher levels of achievement.