Final answer:
Lawrence Kohlberg is the psychologist known for his theory of moral development, which discusses how ethical motivation is developed through three stages: preconventional, conventional, and postconventional.
Step-by-step explanation:
The moral development psychologist known for the theory that ethics is tied to ethical motivation is Lawrence Kohlberg. Kohlberg's contribution to moral psychology includes his famous theory of moral development, which outlines how individuals form their understanding of what is morally right and wrong. This understanding evolves through three levels: preconventional, conventional, and postconventional. Kohlberg's theory suggests that ethical behavior is not always aligned with ethical reasoning, acknowledging that a person might not always 'walk the walk' even if they 'talk the talk'. Furthermore, Kohlberg extended upon Piaget's work in cognitive development, considering the stages of moral development as critical from childhood through adulthood.