Early in life he denied the excesses of his parents, and at the age of fourteen joined a monastery in the diocese of Sne, near the modern town of Esna, Egypt.

Theodorus asserted his influence openly (which resulted in reprimands from Pachomius) and generally maintained himself as a prominent figure at Tabennese for several years, despite never being given a position of power in the monastic hierarchy.

Having failed to prove his governing ability and once more in a position no higher than when he had entered the monastery, Theodorus became a personal assistant to Pachomius and remained relatively quiet for some years.

Despite his clear potential and popularity, Pachomius refused to grant Theodorus any kind of authority; though the old man's failing health soon changed things forever.

For eighteen years Theodorus administered from Pachomius’ old headquarters in Phbow, using techniques far more assertive than his predecessors, such as constantly shuffling the offices and locations of the most ambitious monks.

[2] Like those of Pachomius and the other leaders of the Koinonia, Theodorus’ sermons were recorded by his followers and some chronicles of his correspondence with contemporary Christian figures have survived intact.

A variety of subjects are covered in these texts, though few passages offer any insight beyond the well-known facts that Theodorus greatly admired Pachomius and endorsed a very ascetic lifestyle for the brothers whom he guided.

Certainly these texts all offer insight into the values of the Pachomian monastic system as a whole and early Christianity itself, but little is intrinsically evident about the man who penned them.

Most of the letter consists of sayings Ammon heard from brothers who had personally interacted with Pachomius and Theodorus, much of which is praise for the two men with little real substance.

Although Pachomius was unable to easily communicate with him, he appointed this new Theodorus as the housemaster for the strangers who were also coming to become monks with him in Phbow, and gave him full authority over those who spoke Greek.

Theodorus the Alexandrian eventually learned Coptic and was able to communicate with Pachomius and serve as the official translator of the Koinonia, but the community he administered always remained semi-autonomous from the main population of the monastery.