B.F. Skinner: (1904-1990) with his Behaviorism theory is the number one in Kendra Van Wager's "10 most influential Psychologist" article-written in 2002. After that she listed, sequentially, Sigmund Freud, Albert Bandura, Jean Piaget, Carl Rogers, William James, Eric Erickson, Ivan Pavlov, Kurt Lewin.
Skinner's research into human behavior concerned conditional reflex and recommended psychological conditioning as a method of improving society. His theories were expansions on John B. Watson (1874-1956) ideas of behaviorism. Watson was a Johns Hopkins professor until 1908. In 1920 he left the field to go into the business of advertising.
Sigmund Freud: (1856-1939) regardless of his second place stature as listed by the author of the paper I read, is by far the most well known psychiatrist and by far the most controversial. He made waves wherever he went and, it seems, with each new book or lecture he gave. He founder the field of psychoanalysis, where attempts are made to find out what motivates the patient to act and to think and to behave as they do; and the method of detection was to get into the inner being of the person and analyze his subconscious, the hidden part of his conscious being.
Jean Piaget: 1896-1980 the Swiss child psychologist, wanted to know how knowledge grew. He was interested in the mathematical and the scientific concepts children form, and in how their minds developed. The same method of learning, he taught, is the same method that person will use throughout his life. Thus, as he saw it, each individual had a certain amount of control of how he learned, and that depended on his ability and how it was applied. Choice one makes early in life influences him throughout his life.
Carl Rogers: (1902-1987) He was a U.S. psychologist who learned at Columbia University in New York. His expertise is in the field of "client-centered or non-directive' psychotherapy and his work with 'humanistic" psychology. In other words he is less a director than a psychologist who attempts to get the patient to figure out his own problems by talking them out. This was the forerunner of 'group therapies.' Humanistic psychology is a more aligned approach to the values and ethics of the person and less about behaviorism and other scientific methods. It is somewhat a reigning in of some of the outlandish' means of previous therapy.
William James: (1842-1910) This psychologist was also a U.S. Psychologist and his legacy is pragmatism. Or the furthering of the ideas of C.S. Peirce, the real founder of pragmatism-the practical use of knowledge.
Eric Erikson: (1902-1994) Erikson was a German psychoanalyst who trained in Vienna by A. Freud, an Austrian-British psychiatrist, and daughter of Sigmund Freud. She was the founder of child psychiatry and, for the most part continued the work of her father. Erikson work was mainly with personality development.
Ivan Pavlov: (1884-1936) Pavlov was a Russian physiologist who started the psychological theory of conditioned reflex-the hungry dog salivating at the sound of a bell experiment is his most important legacy. He went on to do other work and in 1904 won the Nobel prize for work on the digestive systems.
Kurt Lewin: (1890-1947) The tenth of this list was a German-U.S. social psychologist who believed that a human behavior has much to do with the environment he grows up in.
Born December 4th,1925,in Alberta, Canada and according one source, is possibly still working at Stanton University. He has taught there for several years. In 1959 he published a book ADOLESCENT AGGRESSION. He is a past president of APA (American Psychiatric Association).
Merriam-Webster's Collegiat Encyclopedia.