Saint Margaret Mary Alacoque (1647–1690) was a French nun and mystic known for her devotion to the Sacred Heart of Jesus. She experienced visions of Jesus, revealing his love and asking for devotion to his Sacred Heart. Despite initial skepticism, her revelations gained acceptance, and the Feast of the Sacred Heart became a significant Catholic celebration. Margaret Mary Alacoque faced challenges within her religious community but remained steadfast in her devotion. Canonized in 1920, she is revered for promoting the practice of the Sacred Heart devotion, emphasizing love, compassion, and the transformative power of a personal relationship with Jesus.