Final answer:
Lawrence Kohlberg is the psychologist known for creating the theory of Stages of Moral Development, where moral reasoning progresses through three levels.
Step-by-step explanation:
The American psychologist best known for the theory of Stages of Moral Development is Lawrence Kohlberg. He developed a theory that suggests our moral reasoning develops through three levels: pre-conventional, conventional, and post-conventional. Kohlberg presented moral dilemmas, such as the Heinz dilemma, to study subjects of different ages to understand how they determined what is right and wrong.