Søren Kierkegaard (1813–1855) was a Danish philosopher who contributed greatly to existentialism. Kierkegaard seemed to believe in the idea of "subjective truth"—that is, the relationship one has with what he believes supercedes than the construct of the belief system itself. (For example, it is more important to live by the teachings of one's religion than to simply believe in them.)
Kierkegaard wrote under various pseudonyms, including Johannes de silentio for Fear and Trembling, as well as A, B and Judge William in various parts of Either/Or. His use of psudonyms wasn't to conceal his authorship, however, but to represent different points of view and seperate his own philosophical views from other explorations. He writes:
In the pseudonymous works, there is not a single word which is mine.
Kierkegaard used different names to represent different viewpoints.
Name: Sóren Aabye Kierkegaard
Pseudonyms: Johannes de silentio,
Born: May 5, 1813, Copenhagen, Denmark
Died: November 11, 1855, Copenhagen