Ancient philosophers like Aristotle, Socrates and Plato contemplated the meaning of happiness and what it means to have a good life and if life is worth living.
Christianity taught that true happiness is found in the afterlife. They spoke about living a virtuous life and a life that is free of sin.
Age of enlightenment or the intellectual movement believed that moral actions and humanity maximized happiness and that everyone was of equal value.
William James created the theory of pragmatism and principles of psychology and Norman Peale published a book about the power of positive thinking.
Abraham Maslow and Carl Rogers believed that Humanistic psychology should be based on the study of self-growth, self-actualization, and human potential.
Martin Seligman became the president of American Psychological Association and introduced positive psychology.