or ALE'XIUS I. COMNE'NUS (Ἄλεξις , or Ἀλέξιος Κομνηνός), emperor of Constantinople, was most probably born in A. D. 1048. He was the son of John Comnenus, and the nephew of the emperor Isaac Comnenus, and received a careful education from his mother Anna. He accompanied the emperor Romanus Diogenes in the war against Alp-Arslán, sultan of the Turks-Seljuks, and was present at the battle of Malazkerd, where this emperor was made a prisoner by the sultan. After the deposition of Romanus Dio genes in 1071, Alexis Comnenus and his elder brother Isaac joined the party of the new emperor, Michael VII. Ducas, who employed Alexis against the rebels who had produced great disturbances in Asia Minor. In this war Alexis distinguished himself as a successful general, and showed that extraordinary shrewdness which afterwards became the principal feature of his character. He defended Michael VII. against the rebel Nicephorus Botaniates, but the cause of Michael having become hopeless, he readily joined the victorious rebel, who became emperor under the title of Nicephorus III. in 1077. The authority of Nicephorus III. was disobeyed by several rebels, among whom Nicephorns Bryennius in Epeirus was the most dangerous; but Alexis defeated them one after the other, and the grateful emperor conferred upon him the title of " Sebastos." Alexis was then considered as the first general of the Byzantine empire, but his military re nown made him suspected in the eyes of the emperor, who kept him at Constantinople and tried to get rid of him by base intrigues. But Alexis opposed in trigues to intrigues, and as he was not only the most gallant, but also the most artful among his shrewd countrymen, he outdid the emperor, who at last gave orders, that his eyes should be put out. Alexis now fled to the army on the Danube, and was proclaimed emperor by the troops. Assisted by his brother Isaac, who acted with great generosity, Alexis marched to Constantinople, obtained possession of the city by a stratagem, deposed the emperor, and ascended the throne in 1081.

The Byzantine empire was then at the point of ruin. While Alexis carried on the war against the rebel Nicephorus Bryennius, and afterwards during his forced sojourn at Constantinople, and the time of his differences with Nicephorus III., Melek-Shah, the son of Alp-Arslán, and the greatest prince of the Seljuks, had conquered the Byzantine part of Asia Minor, which he ceded to his cousin Solimán. The Bulgarians threatened to invade Thrace, and Robert Guiscard, duke of Apulia, with a mighty host of Norman knights, had crossed the Adriatic and laid siege to Durazzo, the ancient Dyrrachium. In this critical position Alexis evinced extraordinary activity. He concluded peace with the Seljuks, ceding Asia to them; he made an alliance with Venice and Henry IV., emperor of Germany; and he sold the sacred vessels of the churches to pay his troops. His struggle with the Normans was long and bloody, but famine, diseases, civil troubles, and a powerful diversion of Henry IV., compelled the Normans to leave Epeirus in 1084. During this time the Seljuks had recommenced hostilities, and threatened to block up Constantinople with a fleet constructed by Greek captives. In this extremity Alexis implored the assistance of the European princes.

The conquest of Jerusalem by the Seljuks, the interruption of the pious pilgrimages to the holy grave, and the vexations which the Christians in the East had to endure from the infidels, had produced an extraordinary excitement among the nations in Europe. The idea of rescuing the town of our Saviour became popular; the pope and the princes shewed themselves favourable to such an expedition, and they resolved upon it after the ambassadors of Alexis had related to them at Piacenza in 1095 the hopeless state of the Christians in Asia. The first Crusaders appeared in Constantinople in 1096. They were commanded by Peter the Hermit and Walter the Pennyless, and were rather a band of vagabonds than an army. Alexis hastened to send them over to Asia, where they were massacred by the Turks. Soon after them came a powerful army, commanded by Godfrey of Bouillon, and their continued stay in the neighbourhood of Constantinople gave occasion to serious differences between the Latins and the Greeks. However Alexis, by the alternate use of threats and persuasions, not only succeeded in getting rid of the dangerous foreigners by carrying them over to Asia, but also managed the pride of Godfrey of Bouillon and his turbulent barons with so much dexterity, that they consented to take the oath of vassalage for those provinces which they might conquer in Asia, and promised to restore to the emperor the Byzantine territories, which had been taken by the Seljuks. In his turn he promised to assist them in their enterprise with a strong army, but the dangerous state of the empire prevented him from keeping his word. However, in proportion as the Crusaders, in 1097, advanced into Asia, Alexis followed them with a chosen body, and thus gradually reunited with his empire Nicaea, Chios, Rhodes, Smyrna, Ephesus, Sardes, and finally all Asia Minor. The descendants of Bohemond, prince of Antioch, did homage to Alexis, to whom they restored Tarsus and Malmistra. During the latter years of his reign, Alexis was occupied with consolidating the domestic peace of his empire, which was then often disturbed by religious troubles. He died in 1118, at the age of seventy, and his successor was his son John, generally called Calo-Joannes.