John of the Cross was a Spanish mystic and poet born in 1542. He is best known for his writings on the spiritual journey and the union of the soul with God. A key figure in the Counter-Reformation, he co-founded the Discalced Carmelites with Teresa of Ávila, emphasizing a return to a more austere and contemplative form of religious life. His most famous works include "The Dark Night of the Soul" and "The Ascent of Mount Carmel," which explore themes of spiritual purification and the deepening of faith. John of the Cross was canonized as a saint in 1726 and is recognized as a Doctor of the Church for his contributions to Christian mysticism.