Martin Heidegger (26 September 1889 – 26 May 1976) was a German philosopher and is widely acknowledged to be one of the most original and important philosophers of the 20th century, while also one of the most controversial. His thinking has contributed to such diverse fields as phenomenology (Merleau-Ponty), existentialism (Sartre, Ortega y Gasset), hermeneutics (Gadamer, Ricoeur), political theory (Arendt, Marcuse, Habermas), psychology (Boss, Binswanger, Rollo May), and theology (Bultmann, Rahner, Tillich). His critique of traditional metaphysics and his opposition to positivism and technological world domination have been embraced by leading theorists of postmodernity (Derrida, Foucault, and Lyotard).
His first and best known book, Being and Time (1927) is one of the central philosophical works of the 20th century. Despite his contributions and influence in diverse fields, the Stanford Encyclopedia of Philosophy cautions, "his thinking should be identified as part of such philosophical movements only with extreme care and qualification. Heidegger was a member and public supporter of the Nazi Party. This involvement in the Nazi movement has invoked a stormy debate. Although he never claimed that his philosophy was concerned with politics, political considerations have come to overshadow his philosophical work.
He joined the Nazi Party on May 1, 1933, ten days after being elected Rector of the University of Freiburg. A year later, in April 1934, he resigned the Rectorship and stopped taking part in Nazi Party meetings, but remained a member of the Nazi Party until its dismantling at the end of World War II. The denazification hearings immediately after World War II led to Heidegger's dismissal from Freiburg, banning him from teaching. In 1949, after several years of investigation, the French military finally classified Heidegger as a Mitläufer or "fellow traveller." The teaching ban was lifted in 1951, and Heidegger was granted emeritus status in 1953; however, he was never allowed to resume his philosophy chairmanship.