David Clarence McClelland (May 20, 1917 – March 27, 1998) was an American psychologist, noted for his work on motivation Need Theory. He published a number of works between the 1950s and the 1990s and developed new scoring systems for the Thematic Apperception Test (TAT) and its descendants. McClelland is credited with developing Achievement Motivation Theory, commonly referred to as "need for achievement" or n-achievement theory. A Review of General Psychology survey published in 2002, ranked McClelland as the 15th most cited psychologist of the 20th century.