Lawrence Kohlberg was an American psychologist best known for his theory of stages of moral development. He was interested in Piaget's theories and studied moral reasoning in children. Kohlberg identified three levels of moral reasoning - pre-conventional, conventional, and post-conventional - consisting of two stages each. His work helped explain how individuals progress through different understandings of fairness and social order. Kohlberg died in 1987 and his stages of moral development theory is still influential in psychology and education today.