David C. McClelland was an American psychologist best known for his work in the field of motivation and personality. He developed the Need Theory, which identifies three primary human needs: achievement, affiliation, and power. His research emphasized how these needs influence behavior and performance in various settings, including education and business. McClelland also contributed to the development of the Thematic Apperception Test (TAT), a projective psychological test used to assess an individual's motivations and personality traits. His work has had a lasting impact on psychology, particularly in understanding how motivation affects human behavior and decision-making.