Sigmund Freud started the development of the theory and practice of psychoanalysis
Willhelm Wundt founded experimental psychology as a discipline and became a pioneer of cultural psychology
Edward Titchener was a prominent psychologist in the United States at an early age and founded the idea of structuralism.
William James' belief in the connection between mind and body led him to develop what has become known as the James-Lange Theory of emotion, which posits that human experience of emotion arises from physiological changes in response to external events.
Watson Rayner wanted to show that Classical Conditioning would work on a human
BF Skinner developed the theory of operant conditioning -- the idea that behavior is determined by its consequences, be they reinforcements or punishments, which make it more or less likely that the behavior will occur again
Abraham Maslow, developed a hierarchy of motivation culminating in self-actualization. Carl Rogers introduced what he called person-centered therapy