Carl Jung (1875 - 1961) was trained as a psychiatrist after receiving his M.D. from Basel University.
He then began research on Psychoanalytic techniques and theories such as word association. In 1906, he began correspondence with Sigmund Freud. The two (2) men met a year later and eventually presented seminars on Psychoanalytic theory together in 1909. Carl Jung was born in Kesswil, Switzerland. Their relationship ended in 1913, when Jung broke away from Freud, resigned his professional positions and began the exploration of his own theories of psychology, religion, and what is known termed the collective unconscious. Although much of his later work is very detailed and intellectual, terms such as introvert and extrovert, parts of his theory, are commonly used expressions today.