William Stern (April 29, 1871 – March 27, 1938), born Ludwig Wilhelm 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. Biography Personal life William Stern was born on April 29, 1871 in Berlin, Germany to Jewish parents, Rosa and Joseph Stern (1837-1890), their only child. He had originally been named Ludwig Wilhelm, but he later dropped his first name and was known simply as William. Stern's father owned a small design studio in Berlin, although the business was not very successful. When Joseph died in 1890, he left his family very little money, and William, who was studying at university, had to take up tutoring to support his sickly mother until her death in 1896. Stern met his future wife, Clara Joseephy, while on a bicycle ride through Berlin. Joseephy's parents were unhappy with the match, as Stern had little money, but Clara persisted despite her parents’ disapproval and the two married early in 1899. They had their first daughter, Hilde, on April 7, 1900, which began the Stern's 18-year long project in child development. The couple also had a son, Günther, in 1902 and another daughter, Eva, in 1904. Stern spent the final five years of his life in exile due to increased antisemitism in Germany. He spent one year in Holland before moving to America to accept a job as a professor