Nicolas Steno was a 17th-century Danish polymath who made foundational contributions to anatomy and geology before entering the Catholic priesthood. Born in Copenhagen, he traveled extensively through Europe, studying medicine and natural sciences in the Netherlands, France, and Italy. His scientific observations, including the discovery of the parotid salivary gland duct and his research into fossil formation, established him as a pioneer of modern stratigraphy. Later in life, he converted from Lutheranism to Catholicism, eventually serving as a titular bishop and the Apostolic Vicar of Nordic Missions.