William of Saint-Thierry was a 12th-century Benedictine monk and theologian known for his mystical writings. He was born around 1085 in the region of Saint-Thierry, France, and became a prominent figure in the monastic reform movement. His works often emphasized the importance of inner spirituality and the love of God. He is best known for his treatises on the Song of Songs and his correspondence with other notable figures, such as Bernard of Clairvaux. William's writings contributed to the development of medieval mysticism and the understanding of the relationship between the soul and God.