Charles D. Spielberger is an American psychologist best known for his work in the field of personality and emotion. He developed the State-Trait Anxiety Inventory, a widely used tool for measuring anxiety levels in individuals. His research has significantly contributed to understanding how anxiety affects behavior and mental health. In addition to his work on anxiety, Spielberger has published numerous articles and books on various psychological topics. He has also been involved in the development of other psychological assessments, further influencing the field of psychology and helping professionals better understand their patients' emotional states.