Soren Kierkegaard was a 19th century Danish philosopher who is widely considered to be the father of existentialism. He is best known for his works Fear and Trembling, The Sickness Unto Death, and Either/Or. Kierkegaard's philosophy focused on the individual's subjective experience and the importance of making choices in life. He believed that life should be lived authentically and passionately, and that individuals should strive to become their true selves.