William Stern, German-American psychologist and philosopher (b. 1871)
William Stern (April 29, 1871 – March 27, 1938), born Louis William Stern, was a German psychologist and philosopher. He is known for the development of personalistic psychology, which placed emphasis on the individual by examining measurable personality traits as well as the interaction of those traits within each person to create the self.

Stern also coined the term intelligence quotient, or IQ, and invented the tone variator as a new way to study human perception of sound. Stern studied psychology and philosophy under Hermann Ebbinghaus at the University of Berlin, and quickly moved on to teach at the University of Breslau. Later he was appointed to the position of professor at the University of Hamburg.

Over the course of his career, Stern wrote many books pioneering new fields in psychology such as differential psychology, critical personalism, forensic psychology, and intelligence testing. Stern was also a pioneer in the field of child psychology. Working with his wife, Clara Joseephy Stern, the couple kept meticulous diaries detailing the lives of their 3 children for 18 years. He used these journals to write several books that offered an unprecedented look into the psychological development of children over time.