François-Isidore Gagelin was a 19th-century French Catholic priest and missionary belonging to the Paris Foreign Missions Society. Born in Montperreux in 1799, he traveled to Vietnam in 1821 to perform missionary work. After fleeing to Đồng Nai in 1826, he faced various challenges, including being captured and subsequently released. He eventually surrendered in August 1833, leading to his death by strangulation in Huế. He is recognized as a martyr for his faith.