James, William -
An American (1842 - 1910), One of the fathers of psychology. Author of  'The principles of Psychology' which helped to establish psychology as a science and influence many of the seminal thinkers of that period.
Janet, Pierre - 
French psychiatrist (1859 - 1947), Studied hypnosis with J. M. Charcot and eventually proposed the 'Theory of Dissociation', to account for many psychological problems and also the nature of hypnosis itself.
Jehovah Complex -
Megalomania. Identification with God or supreme being.
Jung, Carl Gustav -
Swiss psychiatrist (1875 -1961), collaborated with Sigmund Freud (1907 - 1912) to expand the theory of psychoanalysis. In 1912 he broke from Freud to develop his own significant branch of psychoanalysis called Analytical Psychology.