The philosophy of Søren Kierkegaard has been a major influence in the development of 20th-century philosophy, especially existentialism and postmodernism. Søren Kierkegaard was a 19th-century Danish philosopher who has been labeled by many as the "Father of Existentialism", although there are some in the field who express doubt in labeling him an existentialist to begin with. His philosophy also influenced the development of existential psychology.