Nathan Schellenberg Kline, M.D. (March 22, 1916 – February 11, 1983) was an American scientist, researcher in the field of psychology and psychiatrist best known for his work with psychopharmacologic drugs. Having been influential in the development of the very first antipsychotic and antidepressant medications in the 1950s, Kline is often regarded as the "father of psychopharmacology."