St. Teresa of Avila was a Spanish mystic and reformer born on March 28, 1515. She is best known for her role in the Carmelite Order, where she established the Discalced Carmelites, emphasizing a return to a more contemplative and austere lifestyle. Her writings on prayer and spirituality, including "The Interior Castle," have had a lasting impact on Christian mysticism. In 1970, Pope Paul VI declared her a Doctor of the Church, recognizing her significant contributions to theology and spirituality. St. Teresa is celebrated for her deep insights into the nature of prayer and her commitment to a life of devotion, making her a key figure in the Counter-Reformation.