Sultan of Syria, born at Damascus; the extension of his empire over Syria led to the Second Crusade, preached by St. Bernard; compelled the Crusaders to raise the siege of Damascus, which he made his capital; called to interfere in the affairs of Egypt, he conquered it, and made it his own, a sovereignty which Saladin disputed, and which Nur ed-Din was preparing to reassert when he died (1117-1178).