William Glasser was an American psychiatrist best known for developing Reality Therapy and Choice Theory. He emphasized the importance of personal responsibility and the role of choices in shaping behavior and mental health. Glasser believed that individuals have the power to control their own lives through the decisions they make. Throughout his career, Glasser wrote several influential books, including The Quality School and Choice Theory: A New Psychology of Personal Freedom. His work has had a significant impact on education, counseling, and psychotherapy, promoting a more positive and proactive approach to mental well-being and interpersonal relationships.