German philosopher Martin Heidegger addressed the central question of human existence full on, by examining how human self-awareness depends on concepts of time and death. His preoccupation with ontology - the form of metaphysical inquiry concerned with the study of existence itself - dominated his work. The central idea of his complex Sein und Zeit (Being and Time) (1927) could be summed up in the phrase "being is'.
Man had to ask himself "what is it to be?' and only by doing this, and standing back from absorption into objects and other distractions, could he actually exist. For Heidegger, the constant fear of death and the anxieties of life helped man to ask this central question - the mystery of life was intimately linked to the individual's confrontation and consideration of the temporary nature of their own existence.
Heidegger also felt that art, like language, was important evidence of existence, something which was a real existence rather than a mere recreation of reality. He opposed technology, which he believed caused alienation, and advocated a return to an agrarian economy in which the individual had a greater role. For many Heidegger's reputation is tainted by his association with Nazism in 1930's Germany; he actively supported Adolf Hitler during the dictator's first years in power and after World War II he was banned by the Allies from teaching and publishing for five years.
Despite this, his work has been widely influential, especially on the thought of twentieth century philosophical giants such as Sartre, Lacan and Derrida.