Born, Alexios was the second son and third child of the sebastokratorIsaac Komnenos, older brother of Byzantine emperorAlexios I Komnenos, and his wife Irene of Alania. As an imperial relative, he bore the title of sebastos. Almost the only details about his life come from the Alexiad, written by his cousin, Anna Komnene. He is first mentioned in the spring of 1106, when he was appointed by his uncle as the military governor of Dyrrhachium, replacing his older brother John. His earlier life and career are unknown, but it is likely that he had previously held other public posts, just like John, who held his first office at the age of 19. At some point, probably around 1094, he married a certain Zoe, whose family is unknown. The post of governor of Dyrrhachium was of major importance. The city was of great importance to the Byzantine Empire, as the "key of Albania" and the main point of entry from Italy into the Balkans, a fact illustrated by the role it played in the Norman invasion in the early years of Alexios I's reign. John had proven himself unreliable, having been accused of plotting against the emperor and suffering a defeat at the hands of the Dalmatians. With the threat of another Norman invasion looming, Emperor Alexios confided this crucial post to Alexios instead, in whom he evidently placed greater trust. At the same time, the emperor continued sending letters to his nephew, impressing upon him the need to keep constant watch on the coasts for the first sign of a Norman invasion. Indeed, in October 1107, Bohemond I of Antioch, emulating his father Robert Guiscard, landed with a strong army at Avlona. Alexios, who had diligently implemented his uncle's instructions, immediately sent news to him. Bohemond laid siege to Dyrrhachium in November 1107, which lasted until the next spring. The Normans employed a large number of siege engines, but the defenders held firm, using Greek fire to destroy them. Anna Komnene praises Alexios' leadership, both for his bravery and for the inspiration he provided to his men. In the meantime, the situation of the besiegers worsened as Emperor Alexios sent detachments to occupy the various passes and prevent the Normans from foraging, while he moved with his army to Devol to await an opportunity to strike against them. As famine, disease, and desertions plagued the Norman army, Bohemond sent envoys to Alexios to negotiate. On instructions from his uncle, Alexios forwarded the envoys to the Emperor, leading to the conclusion of the Treaty of Devol in which Bohemond acknowledged the Emperor's suzerainty and became his vassal. Alexios' subsequent life and career are unknown, as is the date of his death. According to Theodore Balsamon, his wife fell heavily ill shortly after 1130 to a disease deemed incurable by her physicians. In desperation, her family turned to foreign charlatans, who claimed that her illness was due to spells, and proceeded to discover clay poppets, blaming her servants and entourage. The latter were interrogated and even tortured, but to no avail, as the charlatans were responsible for planting these dolls themselves. In the end, as they proved unable to improve her condition, they fled the palace. Some of her relatives and servants who participated in these events were later punished for believing in and abetting sorcery by Patriarch Leo Styppes. The couple probably had a son, named John, known from a single funerary poem, who was a distinguished military commander.
