St. Margaret Mary Alacoque was a French nun born on July 22, 1647, in L'Hautecour, France. She is best known for her devotion to the Sacred Heart of Jesus and played a significant role in promoting this devotion within the Catholic Church. Margaret Mary entered the Visitation Order in 1671 and experienced several mystical visions of Jesus, which inspired her spiritual life and mission. Her most notable contributions include the establishment of the feast of the Sacred Heart and the promotion of the First Friday devotion. St. Margaret Mary was canonized by Pope Benedict XV in 1920, and her feast day is celebrated on October 16.