Richard Lazarus was an influential American psychologist known for his work in the field of stress and coping. He developed the Cognitive Appraisal Theory, which emphasizes how individuals evaluate and respond to stressful situations. His research highlighted the importance of personal interpretation in determining emotional responses. Lazarus also contributed to the understanding of emotions and their role in psychological well-being. He collaborated with Susan Folkman to create the Transactional Model of Stress and Coping, which outlines how people manage stress through various coping strategies. His work has had a lasting impact on psychology and mental health practices.