Prōtostratōr was a Byzantine court office, originating as the imperial stable master. Its proximity to the imperial person led to a highly visible role in imperial ceremonies, and served as a springboard for several capable individuals, like Manuel the Armenian or the future emperors Michael II and Basil I the Macedonian, to reach the highest offices. From the mid-11th century, the post rose in importance, becoming more an honorific dignity for senior members of the court, than an actual office. From the 13th century on, the post could be held by several persons, and ranked eighth in the overall hierarchy of the court. Throughout its history, it was a title often borne by senior military commanders. The female form of the title, given to the wives of the prōtostratores, was prōtostratorissa (πρωτοστρατόρισσα).

Alexios Komnenos was a Byzantine aristocrat and courtier. A son of Andronikos Komnenos and nephew of Emperor Manuel I Komnenos, he rose to the high rank of prōtostratōr in 1167. In 1176 he participated in the Myriokephalon campaign where, following the death of his older brother John, he was raised to the titles of prōtosebastos and prōtovestiarios. Following Manuel's death in 1180, he won the favour, and reportedly became the lover, of Empress-dowager Maria of Antioch. Through her he ruled the Byzantine Empire for two years as de facto regent of the underage emperor Alexios II Komnenos. The aristocracy challenged his dominance, led by the princess Maria Komnene, who plotted to assassinate the prōtosebastos. The plot was discovered and most conspirators arrested, but Maria and her husband fled to the Hagia Sophia, protected by Patriarch Theodosios Borradiotes and the common people of Constantinople.