Douglas McGregor was an American social psychologist best known for his theories on management and motivation in the workplace. He introduced the concepts of Theory X and Theory Y in his 1960 book, "The Human Side of Enterprise." These theories describe two contrasting views of employee motivation and behavior, influencing management practices. McGregor's work emphasized the importance of understanding human needs and motivations in organizational settings. He believed that a positive approach to management, which recognizes employees' potential and encourages participation, leads to better performance and job satisfaction. His ideas have had a lasting impact on management theory and practice.