Nikolai Alexandrovich Berdyaev was a Russian philosopher, theologian, and Christian existentialist who emphasized the existential spiritual significance of human freedom and the human person. Alternative historical spellings of his surname in English include "Berdiaev" and "Berdiaeff", and of his given name "Nicolas" and "Nicholas".

Christian existentialism is a theo-philosophical movement which takes an existentialist approach to Christian theology. The school of thought is often traced back to the work of the Danish philosopher and theologian Søren Kierkegaard (1813–1855) who is widely regarded as the father of existentialism.