Saint 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, which she promoted through her visions and experiences. Margaret Mary joined the Visitation Order and dedicated her life to prayer and contemplation. In 1673, she began receiving revelations about the love of Jesus for humanity, leading to the establishment of the Feast of the Sacred Heart. She passed away on October 17, 1690, and was canonized by Pope Benedict XV in 1920. Her feast day is celebrated on October 16.