Existentialism is timeless—the existentialist way of thinking has been identified in Heraclitus, Socrates, and Augustine. But modern existentialism is identified with the thought of five thinkers: Kierkegaard, Nietzsche, Heidegger, Camus, and Sartre. The wide difference in the religious and political thought of these five philosophers makes it difficult to see existentialism as a school based on a doctrine or worldview. Kierkegaard was religious. Nietzsche and Sartre were atheists. Kierkegaard would have nothing to do with politics; he was disgusted by it. Sartre, Camus, and Heidegger were deeply into politics. They were political theorists as well as political activists. Sartre was a Marxist. Camus was an anti-Marxist and identified as a humanitarian. Heidegger, it is alleged, was close to Nazism. Instead of a common doctrine and worldview, existentialism is a movement based on certain sensibilities regarding individualism and human freedom. The philosophy sees Dostoevsky and Kafka as its chief thinkers.