Martin Heidegger (1889–1976) was a German philosopher known for his contributions to existential phenomenology and his profound influence on 20th-century philosophy, particularly existentialism and postmodernism. Noted for his complex and innovative ideas, Heidegger sought to explore the nature of Being (or existence) through his principal work "Sein und Zeit" ("Being and Time," 1927). In this seminal text, Heidegger investigates the fundamental aspects of human existence, with a focus on concepts such as temporality, care, and authenticity. Heidegger's work is characterized by an exploration of the ways in which human beings relate to their world and the philosophical significance of everyday experiences. While his affiliation with the Nazi Party and service as a rector at the University of Freiburg remain deeply controversial, his thought has nevertheless had lasting impact across a wide range of philosophical schools and disciplines. His ideas have also been influential in fields beyond philosophy, including theology, literary theory, psychology, and environmentalism.