David West Keirsey (; August 31, 1921 – July 30, 2013) was an American psychologist, a professor emeritus at California State University, Fullerton, and the author of several books. In his most popular publications, Please Understand Me (1978, co-authored by Marilyn Bates) and the revised and expanded second volume Please Understand Me II (1998), he laid out a self-assessed personality questionnaire, known as the Keirsey Temperament Sorter, which links human behavioral patterns to four temperaments and sixteen character types. Both volumes of Please Understand Me contain the questionnaire for type evaluation with detailed portraits and a systematic treatment of descriptions of temperament traits and personality characteristics. With a focus on conflict management and cooperation, Keirsey specialized in family and partnership counseling and the coaching of children and adults. Early life, education and professional experience Keirsey was born in Ada, Oklahoma. He moved with his family at the age of two years to Southern California. Drafted by the Army during World War II, he joined the Navy and became a Marine fighter pilot, and served in the Pacific theatre off an aircraft carrier. He earned his bachelor's degree from Pomona College and his master's and doctorate degrees from Claremont Graduate University (then known as Claremont Graduate School). In 1950, he started his career dealing with youth as a counselor at a probation ranch home for delinquent boys. Subsequently, he spent twenty years working in public schools, engaged in corrective interventions intended to help troubled and troublesome children stay out of trouble. Over the next eleven years at California State University, Fullerton, he trained corrective counselors to identify deviant habits of children, parents, and teachers, and to apply techniques aimed at enabling them to abandon such habits. Development of temperament theories Keirsey has written extensively about his model of four temperaments (Artisan, Guardian, Idealist, and Rational) and sixteen role variants. His research and observation of human behavior started after he returned from World War II, when he served in the Pacific as a Marine fighter pilot. Keirsey traced his work back to Hippocrates, Plato and Aristotle. Among his modern influences he counts the works of William James, John Dewey, Ernst Kretschmer, William Sheldon, Jay Haley, Gregory Bateson, Max Wertheimer, Wolfgang Kohler, Raymond Holden Wheeler, Erich Fromm, Alfred Adler, Rudolf Dreikurs, Milton Erickson, and Erving Goffman. He considered himself the last of the Gestalt psychologists. In 1921, Carl Jung published the book Psychological