Bernard was born to the Burgundian nobility and might have inherited a brilliant secular future. At twenty-two, after the death of his mother, he persuaded thirty kinsmen and friends — including all four of his brothers — to enter with him the strict new monastery of Cîteaux, which had been founded fourteen years earlier. The arrival of this band of young noblemen rescued the struggling Cistercian movement and made its future.
Three years later, at twenty-five, he was sent with twelve companions to found a daughter house at Clairvaux ('Clear Valley') in Champagne. He was abbot there for the rest of his life. From this remote monastery — through preaching, the most extensive correspondence of any 12th-century figure, and the force of personal sanctity — he became the most influential man in Europe. He preached the Second Crusade at Vézelay (1146), composed the Rule of the Knights Templar, settled the papal schism of 1130–38 in favour of Innocent II, and saw a former Cistercian disciple elected Pope Eugene III (1145).
His writings — Sermons on the Song of Songs, On Loving God, On Consideration (a manual for Pope Eugene III), the Steps of Humility — combined doctrinal precision with extraordinary tenderness. His Marian piety shaped centuries of Catholic devotion: the prayer Memorare is traditionally attributed to him. Pius VIII declared him Doctor of the Church in 1830; Pius XII, on the 800th anniversary of his death, issued the encyclical Doctor Mellifluus (1953).