Nur ad-Din (nōr äd-dēn) [key], 1118–74, ruler of Syria. He was the son of the conqueror Zangi, and he succeeded to power in 1145. He defeated the Seljuk Turks in Asia Minor and fought with Baldwin III of Jerusalem. His lieutenant Shirkuh barely forestalled the forces of Baldwin's successor, Amalric I, in occupying Egypt. Nur ad-Din built hospitals, mosques, and schools and was notable for his rule of temperance and justice. Aroused by the independent actions of Saladin, Shirkuh's successor, Nur ad-Din was preparing to invade Egypt at the time of his death.