(Ἰσαάκιος ὁ Κομνηνός), emperor of Constantinople (A. D. 1057-1059), and the first of the Comneni who ascended the imperial throne, was one of the most virtuous emperors of the East. [See the genealogical table of the Comneni, Vol. I. p. 820.] he was the elder son of Manuel Comnenus, praefectus totius orientis in the reign of Basil II, whom he lost while still a boy, and was educated, together with his younger brother John, under the care of Basil. Their learning. talents, and moral principles, as much as the merits of their late father, recommended them to the favour of the emperor, and at an early age they were both entrusted with important civil and military functions. Isaac became so distinguished, that, supported by the illustrious name of his family, he succeeded in obtaining the hand of Catharina, or Aicatharina, the daughter of Samuel, or perhaps John Wladislaus, king of the Bulgarians, a lady who, at the time when Isaac made her acquaintance, was a captive at the Byzantine court. During the stormy reigns of the eight immediate successors of Basil II. (Constantine IX., Romanns III., Michael IV., Michael V., Zoe, Constantine X., Theodora, and Michael VI.), who successively occupied the throne during the short period of 32 years, the position of Isaac was often dangerous but he conducted himself with so much prudence, and enjoyed so much of the general esteem, that he not only escaped the many dangers by which he was surrounded, but was considered by the people a worthy successor of their worthless master, Michael VI. The conduct of this emperor was so revoltin, that shortly after his accession in 1056, the principal nobles and functionaries, supported by the clergy and a large majority of the nation, resolved to depose him. They offered the crown to the old Catacalon, a distinguished general who was leader of the conspiracy, but he declined the proposition on the ground of his age and obscure birth, and pointed out Isaac Comnenus as a fit candidate for their choice. Isaac was proclaimed emperor (August 1057) without his knowledge, and was with some difficulty induced to accept the crown. Michael sustained a severe defeat at a place called Hades, and, despairing of success, proposed to Isaac to share with him the imperial power, an offer which the peaceful prince would have accepted but for the interference of Catacalon, who strongly opposed any amicable arrangement, on the ground of the well-known faithlessness of Michael. The latter was soon after compelled to resign, and assume the monastic habit. In his struggle with Michael, Isaac was cordially assisted by his excellent brother John. He rewarded the leaders of the conspiracy with great liberality, but in a manner that showed his good sense, for he sent most of them into the provinces, and conferred such honours and offices upon them as entailed only a moderate degree of power and influence. He divided the important functions of the curopalates between Catacalon and his brother John. The treasury being exhausted, he introduced a system of great economy into all the branches of the administration, showing, by his own example, how his subjects ought to act under such circumstances. In levying new taxes, however, he called upon the clergy also to contribute their share, but they refused to comply with his orders; and the patriarch of Constantinople, Michael Cerularius, had the impudence to say to the emperor: " I have given you the crown, and I know how to take it from you again." Banishment was the reward for this insolence, and death prevented the priest from taking revenge by kindling a rebellion. In several cases Isaac acted rather haughtily, and he sometimes found difficulty in reconciling through his wisdom, those whom he had wounded through his pride. In 1059 he marched against the Hungarians, who had crossed the Danube, land compelled them to sue for peace. This was the only occasion during his reign where he could show that he was the best tactician among the Greeks. The empire recovered visibly under his administration from so many calamities, and great was the grief of the people when, after his return from the Hungarian campaign, he was suddenly attacked by a violent fever, which brought him to the verge of the tomb. Feeling his death approaching, he called for his brother and offered him the crown, but John having declined it, he appointed Constantine Ducas, a renowned general, his future successor. Isaac, however, recovered from his illness, but, to the utmost grief and astonishment of his brother and the people, resigned the crown into the hands of Constantine Ducas, and retired to a convent (December, 1059). His wife and daughter followed his example, and took the veil. Isaac survived his abdication about two years, living in the strictest performance of the duties of a monk. and devoting his leisure hours to learned occupations. The emperor Constantine XI. often visited him in his cell, and consulted him on important affairs; and among the people he was in the odour of sanctity. His death probably took place in 1061. He left no male issue.