Lucia dos Santos (1907–2005), later known as Sister Lucia, was one of the three shepherd children who witnessed the Marian apparitions at Fatima, Portugal, in 1917. Born in Aljustrel, a small village near Fatima, she was the youngest of seven children in a devout Catholic family. Along with her cousins Francisco and Jacinta Marto, she experienced six apparitions of the Virgin Mary at the Cova da Iria, where Mary delivered messages of prayer, penance, and devotion, particularly through the Rosary. Lucia became the primary communicator of these messages, as Francisco and Jacinta both passed away during the 1918 influenza pandemic.

After the apparitions, Lucia continued to spread the message of Fatima, entering religious life to deepen her commitment. She joined the Sisters of Saint Dorothy and later became a Discalced Carmelite nun, taking the name Sister Maria Lucia of Jesus and the Immaculate Heart. Throughout her life, she corresponded with Church authorities, including popes, about the secrets of Fatima, which included visions of Hell, the prediction of World War II, and a call for the consecration of Russia to Mary’s Immaculate Heart. Her writings, particularly her memoirs and letters, were instrumental in spreading the devotion to Our Lady of Fatima worldwide.

Sister Lucia lived a long and quiet life in the Carmelite convent in Coimbra, Portugal, where she passed away on February 13, 2005, at the age of 97. Her cause for canonization began in 2008, and Pope Francis declared her Venerable on June 22, 2023, recognizing her heroic virtues.