Origin and early career under Manuel I
Alexios was the second son and the last of five children of the sebastokratōr Andronikos Komnenos, himself the second son of Emperor John II Komnenos and Irene of Hungary. The origin of Alexios' mother, also named Irene, is unknown. The court poet, Theodore Prodromos, composed a laudatory poem to celebrate his birth.
In his prosopographical study of the Komnenoi, the Greek scholar, Konstantinos Varzos, placed his birth on Easter Day 1135 (or possibly 1134 or 1136), as he was old enough to participate in a campaign in 1149/50. Alexios' father died in August 1142, only a little while after his older brother (also named Alexios). The two brothers were on a campaign with their father, John II, and their other brothers in southern Asia Minor, and probably died of the same illness. This provided the occasion for another poem by Prodromos, in which young Alexios is referred to as the only solace for his bereaved mother. The Prosopography of the Byzantine World database, on the other hand, interprets the poems by Prodromos as indicating that Alexios was born in 1142, during his father's absence on the campaign that cost his life.
When John II died in 1143, his two remaining sons were Isaac and Manuel I Komnenos. Although the younger of the two, because of the army's support, Manuel eventually became emperor. Although Alexios' mother, the sebastokratorissa Irene, suffered repeated disgrace and imprisonment at the hands of Manuel, the emperor showed great favour to her sons, particularly Alexios' older brother John. In c. 1149/50, like all young Byzantine aristocrats, the young Alexios was required to begin his military training and accompany his uncle, Emperor Manuel, on campaign. However, no details of his early military career are known. In c. 1153/4 he married Maria Doukaina, whose exact parentage is unknown. Together they had at least four children: a son Andronikos, a daughter Irene, and a son and daughter whose names are unknown.
The first recorded instance of Alexios attending a public function was at a synod at the imperial Palace of Blachernae, on 12 May 1157, with his brother John. He also participated in the synod of March 1166, also along with John. In both cases, Alexios is recorded among the imperial relatives, with no rank or title. In May/June 1167, following the dismissal and banishment of the prōtostratōr, Alexios Axouch, Alexios Komnenos assumed this high office. He appears with this rank at the synod in February 1170 that was convened to sit judgment against John Eirenikos. Sometime during his tenure as prōtostratōr, Alexios fell gravely ill, and his wife donated a richly embroidered veil to the Church of the Saviour at the Chalke Gate, an occasion celebrated by an anonymous court poet.
Like most of the Byzantine aristocracy, Alexios took part in the campaign that led to the disastrous Battle of Myriokephalon in September 1176. His brother John was one of the battle's casualties. Alexios, as the last remaining son of Manuel's brothers, succeeded him in his titles of prōtosebastos and prōtovestiarios. Like John before him, these titles raised Alexios to the pinnacle of the Byzantine court. As prōtosebastos, he was the most senior of the sebastoi, a group which, since the days of Alexios I Komnenos, denoted the most senior members of the court, usually close relatives or special favourites of the emperor. Furthermore, as prōtovestiarios, he was the "titular head of the imperial household", with important ceremonial and diplomatic duties. His previous post of prōtostratōr went to another Alexios, son of Andronikos Komnenos Vatatzes. Soon after Alexios' promotion, his wife died, and his son Andronikos was mortally injured after falling from his horse. The poet Gregory Antiochos wrote a lament on the occasion.
In spring 1178, Alexios led an embassy to France. His first mission concerned the marriage of his cousin Eudokia—daughter of his paternal uncle Isaac—to Ramon Berenguer III, Count of Provence, brother of King Alfonso II of Aragon. The opposition of the German emperor Frederick Barbarossa aborted the marriage, and Eudokia was married instead to William VIII of Montpellier. Alexios then proceeded to Paris, to escort Agnes, a daughter of King Louis VII of France and the prospective bride of Manuel's son and heir Alexios II Komnenos, back to Byzantium. The embassy left Paris on Easter 1179, and returned via Italy to Constantinople, where Agnes and Alexios II were betrothed.
