Isaac I (Isaac Comnenus) (ī´zək kŏmnē´nəs), c.1005–1061, Byzantine emperor (1057–59), first of the Comnenus dynasty. Proclaimed emperor by the army, he deposed Michael VI, who had succeeded Theodora (reigned 1055–56), and sent him into a monastery. Although at first received with enthusiasm at Constantinople, Isaac soon lost popularity with the aristocracy and, because of his confiscation of ecclesiastic property, with the church and the patriarch Cerularius, who was exiled. In 1059, after an unsuccessful campaign against the Pechenegs, Isaac abdicated for reasons of health and retired to a monastery. Constantine X (Constantine Ducas) was his successor. After the reigns of Romanus IV, Michael VII, and Nicephorus III, the Comnenus dynasty returned to the throne with Isaac's nephew Alexius I.