Alexios is the first known member of the Mosele/Mousele family of Armenian origin. In 790, he was the commander of the Vigla guard regiment, being the first known occupant of the office. In September of that year, he was sent by the Empress-regent Irene of Athens (r. 797–802) to deal with the soldiers of the Armeniac Theme, who had refused to swear an oath of loyalty which placed her before her son, Emperor Constantine VI (r. 780–797). The Armeniacs, however, imprisoned their own general Nikephoros, declared Mosele their new commander, and acclaimed Constantine as the sole emperor. At the news of this, the other themes of Asia Minor followed suit in deposing their commanders and affirming Constantine as sole emperor.
The thematic troops then assembled in Bithynia, where they demanded from Irene to release Constantine from his de facto house arrest. Bowing to the pressure from the troops, Irene released her son. Emperor Constantine shortly after assumed the reins of government, dismissing Irene's counselors and confining her to a palace in Constantinople. Mosele was confirmed as the Armeniacs' commander by Constantine, and later summoned to Constantinople and raised to the rank of patrikios. Constantine, however, soon proved incapable to rule the empire effectively, and the military successes, which the soldiers who supported him had hoped for, did not materialize. In January 792, moreover, he recalled his mother from her banishment, restored her to her titles and position of co-ruler, and demanded from the army to acclaim her along with him. The Armeniacs once again refused to comply, and demanded the return of Mosele from Constantinople. Despite having guaranteed his personal safety, Constantine, who suspected him of designs on the throne, had him flogged, tonsured, and imprisoned.
This was followed soon after by the disastrous defeat of the Byzantine army, led by the emperor himself, at the Battle of Marcellae against the Bulgars. As the imperial army grumbled and even the usually loyal tagmata plotted to replace him, Constantine, on the advice of his mother and her eunuch adviser Staurakios, had Mosele blinded. Constantine's uncle, Nikephoros, whom the tagmatic soldiers planned to make emperor, was also blinded, while four other uncles had their tongues cut. At the news of this, the Armeniacs rose in open rebellion. They defeated a loyalist army in November, and were defeated only in May 793 by an expedition under Constantine himself.
- Garland, Lynda (1999). Byzantine Empresses: Women and Power in Byzantium, AD 527–1204. New York and London: Routledge. ISBN 978-0-415-14688-3.CS1 maint: ref=harv (link)
- Kaegi, Walter Emil (1981). Byzantine Military Unrest, 471–843: An Interpretation. Amsterdam: Adolf M. Hakkert. ISBN 90-256-0902-3.CS1 maint: ref=harv (link)
- Kazhdan, Alexander, ed. (1991). The Oxford Dictionary of Byzantium. New York and Oxford: Oxford University Press. ISBN 978-0-19-504652-6. Missing or empty
|title=(help)CS1 maint: ref=harv (link)
- Treadgold, Warren (1997). A History of the Byzantine State and Society. Stanford, California: Stanford University Press. ISBN 0-8047-2630-2.CS1 maint: ref=harv (link)
- Winkelmann, Friedhelm; Lilie, Ralph-Johannes; Ludwig, Claudia; Pratsch, Thomas; Rochow, Ilse (1999). "Alexios Musele(m) (#193)". Prosopographie der mittelbyzantinischen Zeit: I. Abteilung (641–867), 1. Band: Aaron (#1) – Georgios (#2182) (in German). Berlin and New York: Walter de Gruyter. pp. 58–59. ISBN 978-3-11-015179-4.CS1 maint: ref=harv (link)