(Ἰσαάκιος ὁ Ἄγγελος), emperor of Constantinople (A. D. 1185 --1195), was the eldest son of Andronicus Angelus, and was born in the middle half of the 12th century. Belonging to one of the great Byzantine families and descended, through his grandmother Theodora, from the imperial family of the Comneni, he held several offices of importance in the reign of the emperor Manuel Comnenus; but his name remained obscure, and the emperor Andronicus Comnenus, the exterminator of the Greek nobility, despised to kill such a harmless being, although he put his father Andronicus Angelus to death. The weak-minded Isaac became, nevertheless, the cause of the deposition and miserable end of Andronicus Comnenus. In the summer of 1185 the emperor retired for a short time to one of his country seats in Asia, appointing one Hagiochristophorites his lieutenant in Constantinople during his absence. This officer gave orders to put Isaac to death, because his name began with an I; and there was a silly belief among the people that Andronicus would be ruined by somebody whose name began with an I. Isaac was fortunately apprized of the bloody design of the emperor's lieutenant, but had barely time to escape from his palace, and to avail himself of the sanctuary of the church of St. Sophia. A dense crowd soon filled the church : Isaac implored their assistance; and the numerous enemies of Andronicus, exerting themselves to kindle a revolt in favour of any one persecuted by that cruel emperor, the fickle people of Constantinople suddenly took up arms, killed the officers despatched by Hagiochristophorites to put Isaac to death, and proclaimed the latter emperor of Constantinople (A. D. 1185). Andronicus hastened to his capital, but it was too late he was seized by the mob, and, by order, or at least with the consent of Isaac, perished in the miserable manner which is related in his life. [ANDRONICUS I.]

No sooner was Isaac firmly established on the throne than lie began a life which Gibbon thus describes: --" He slept on the throne, and was awakened only by the sound of pleasure: his vacant hours were amused by comedians and buffoons ; and even to these buffoons the emperor was an object of contempt: his feasts and buildings exceeded the examples of royal luxury, the number of his eunuchs and domestics amounted to twenty thousand, and the daily sum of four thousand pounds of silver would swell to four millions sterling the annual expense of his household and table. His poverty was relieved by oppression, and the public discontent was inflamed by equal abuses in the collection and the application of the revenue." Shortly after his accession Isaac was involved in a dreadful war with the Bulgarians, which arose under the following circumstances:--After the conquest by Basil II. of the powerful Bulgarian kingdom, which extended over the greater part of the Thracian peninsula, the Bulgarians continued to live under the sway of the Byzantine emperors, till Peter and Asan, two brothers, who were descended from the ancient kings of Bulgaria, took up arms in order to deliver their country from the insupportable oppression and rapacity of Isaac. They were successful--they penetrated as far as Thessalonica--they defeated and made prisoner Isaac Sebastocrator, the Greek generalissimo, in a pitched battle; and at last Asan was acknowledged as king of Bulgaria Nigra, or that country which is still called Bulgaria. In this war the Bulgarians were assisted by the Blachi or Moro-Vlachi, the descendants of ancient Roman colonists in the mountainous parts of Thessaly and Macedonia, who were likewise driven to despair by the rapacious emperor, and who finally left their homes and emigrated into the countries beyond the Danube (Dacia), where, mixed with Slavonian tribes, they continued to live, and still live, as Wallachians. However, some of them remained in their native mountains in Thessaly and Macedonia: they were the ancestors of the present Kutzo-Wallachians. In a second war with the Bulgarians, the Greek arms obtained a decisive victory (1193); but Isaac was, nevertheless, obliged to recognise the successor of Asan, Joannicus or Joannes. Isaac was more successful against William II., the Good, who was compelled, in 1187, to give up the conquests which he had made two years previously in Epeirus, Thessaly, and Macedonia. In 1189 the emperor Frederic I. of Germany appeared on the northern frontier of the Byzantine empire, with an army of 150,000 men, on his way to the Holy Land. Iin spite of the menaces of Isaac., the emperor quietly advanced, took up his winter-quarters at Adrianople, and crossed the Bosporus, deelining both to help the Bulgarians against the Greeks, and the Greeks against the Bulgarians.

Isaac was so terrified by the emperor's march through his dominions, and the success of the other crusaders in Syria and Palestine, that he sent an ambassador to Saladin offering him his alliance against the Latins, which, however, Saladin declined, because Isaac demanded the restitution of the holy sepulchre. Besides Bulgaria, Isaac lost the island of Cyprus, where Alexis Comnenus had made himself independent, but was deprived of his conquest by Richard Coeur de Lion of England (1191), who in 1192 ceded it to king Guido of Jerusalem; and Cyprus was never again united to the Byzantine empire. Isaac, continuing to make himself despised and hated by the Greeks, a rebellion broke out at Constantinople while he was hunting in the mountains of Thrace; and Alexis, the younger brother of Isaac, was raised to the throne. On this news, Isaac fled without daring to implore the assistance of any one. Arrived at Stagyra in Macedonia, he was arrested and brought before Alexis, who ordered his eyes to be put out, and confined him in a prison (1195). [ALEXIS III.] Alexis, the son of Isaac, fortunately escaped, fled to Italy, and succeeded in rousing the Latin princes to a war against Alexis III., which resulted in the capture of Constantinople in 1203, and the restoration of the blind Isaac, who reigned, together with his son [ALEXIS IV], till the following year, 1204, when Alexis IV. was dethroned and killed by Alexis Ducas Murzuphlus [ALEXIS V.], who usurped the throne, and kept it during two months, when he, in his turn, was deposed by the Latins. Murzuphlus spared the life of Isaac, who, however, did not long survive the melancholy fate of his youthful and spirited son. (Nicetas, Isaacius Angelus; Isaacius et Alexis filius ; the Latin authorities quoted under Alexis III., IV., V.]