Athanasius was a Byzantine monk and a grandson of Theodora, wife of Justinian I. The main sources about him are John of Ephesus, Michael the Syrian and Bar-Hebraeus.
Athanasius was son to an unnamed daughter of Theodora, wife of Justinian I.John of Ephesus first mentions him as "Athanasius, the son of queen Theodora's daughter". He received a religious education, his mentors being Amantius and Sergius of Tella. The former was a monk from Edessa, the latter served as a Syriac Patriarch of Antioch from 544 to 546. Both mentors were Monophysites.
Athanasius later became a Tritheite and a disciple of John Asconaghes. R. Payne Smith explains the origins of their belief system and Athanasius' affiliation to it:"This Philoponus, called also John Grammaticus, a very learned Aristotelian of Alexandria, is generally looked upon as their founder, but really he only defended their heresy, by an argument deduced from an exposition of what 'substance' is, according to the doctrines of his great master, Aristotle. Their real founder was a certain obscure John Ascunages, whose creed is preserved by Bar-Hebraeus: 'I acknowledge one nature of Christ the Incarnate Word, but in the Trinity I reckon the natures and substances and Godheads according to the number of the persons.' But for the learning of Philoponus the sect would probably have expired with its founder; but an adventitious importance was further given to it by its being joined by Athanasius, the son of Theodora's daughter, whose great wealth was freely expended in obtaining converts.