John of the Cross was a Spanish mystic and poet born in 1542. He is best known for his role in the Carmelite reform movement alongside Teresa of Ávila. His writings focus on the soul's journey toward union with God, emphasizing the importance of spiritual purification and contemplation. His most famous works include "The Dark Night of the Soul" and "The Ascent of Mount Carmel," which explore themes of suffering and divine love. John of the Cross was canonized as a saint in 1726 and declared a Doctor of the Church in 1926, highlighting his significant influence on Christian mysticism.