Lawrence Kohlberg was a Harvard professor known for his theory of moral development. He proposed that morality develops through six stages across three levels - pre-conventional, conventional, and post-conventional. At the pre-conventional level, children's morality is based on obedience and self-interest. The conventional level involves conforming to social norms and rules. Finally, at the post-conventional level, morality is based on abstract principles of justice and social contracts. Kohlberg's theory suggests morality grows increasingly complex as individuals develop through these six stages.