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John of the Cross (1542-1591) was a Spanish Catholic priest and poet who founded the Discalced Carmelites. He was a disciple of Teresa of Ávila, who was the founder of the Order of the Discalced Carmelites. John of the Cross wrote several works of mystical theology, including The Ascent of Mount Carmel and The Dark Night of the Soul. He is considered one of the greatest Christian mystics.