Louis Leon Thurstone was an American psychologist born on May 29, 1887, in Chicago, Illinois. He is best known for his work in psychometrics and intelligence testing. Thurstone developed the Thurstone Scale, a method for measuring attitudes, and contributed significantly to the understanding of multiple intelligences through his theory of primary mental abilities. Thurstone's research emphasized that intelligence is not a single entity but consists of several distinct factors, such as verbal comprehension and numerical ability. His work laid the foundation for later theories of intelligence, influencing the field of psychology and education. He passed away on September 30, 1955.