Barbara (Greek Barbara, 'foreign'; Hebrew unknown) is — per the universal medieval tradition (preserved in the 7th-century Greek Acts of Barbara) — a young virgin of Nicomedia (the eastern co-capital of Diocletian's tetrarchy and the imperial seat from which the Great Persecution was launched). She was the daughter of a wealthy pagan noble named Dioscorus, who — knowing his daughter's extraordinary beauty — kept her enclosed in a tall tower with two windows to protect her from the world.
While Dioscorus was away on a long journey, Barbara directed the workmen building a small bathhouse extension to her tower to add a third window — that there might be three windows in the bathhouse to represent the three Persons of the Trinity. She was secretly catechized by a Christian who had reached her in disguise as a doctor. When Dioscorus returned and discovered both the third window and her conversion, he denounced her himself to the Roman provincial authorities. She was tortured at length: scourged, the rack, the iron combs, the burning torches; each night her wounds were healed by an angel.
Finally Dioscorus himself was permitted by the Roman authorities to behead her. As he was returning home from the execution he was killed by a sudden lightning strike (the celebrated lightning-vengeance that became the iconographic emblem of her cult and the basis of her universal patronage of artillery, gunpowder, and sudden death).
The historicity of Barbara has been much debated in modern critical scholarship — the 1969 revision of the universal Roman calendar removed her from the universal calendar precisely because of doubts about historicity. But the medieval cult was one of the most extensive of any saint in the entire Catholic tradition: she is one of the Fourteen Holy Helpers (the central late-medieval German devotional cluster); her patronage extends across artillery, gunpowder, mining, mountaineering, fireworks, the entire range of professions involving explosives or sudden danger; and especially her patronage of sudden unprovided death — the great medieval Catholic devotion of asking St. Barbara to obtain the grace of receiving the Last Sacraments before any sudden death — has been a major Catholic devotional theme for over a millennium.