Saint Theophilus lived in Egypt in the fourth century, and is mentioned in the Life of Saint Onuphrius.

After he had buried Saint Onuphrius, Saint Paphnutius came upon an oasis which impressed him with its beauty and abundance of fruit-bearing trees. Four youths inhabiting this place came to him from out of the wilderness. The youths told Abba Paphnutius that in their childhood they had lived in the city of Oxyrhynchus (Upper Thebaid) and they had studied together. They had burned with the desire to devote their lives to God. Making their plans to go off into the desert, the young men left the city and after several days’ journey, they reached this place.

A man radiant with heavenly glory met them and led them to a desert Elder. “We have lived here six years already,” said the youths. “Our Elder dwelt here one year and then he died. Now we live here alone, we eat the fruit of the trees, and we have water from a spring.” The youths gave him their names, they were Saints John, Andrew, Heraclemon and Theophilus (Dec. 2).

The youths struggled separately the whole week long, but on Saturday and Sunday they gathered at the oasis and offered up common prayer. On these days an angel would appear and commune them with the Holy Mysteries. This time however, for Abba Paphnutius’ sake, they did not go off into the desert, but spent the whole week together at prayer. On the following Saturday and Sunday Saint Paphnutius together with the youths was granted to receive the Holy Mysteries from the hands of the angel and to hear these words, “Receive the Imperishable Food, unending bliss and life eternal, the Body and Blood of the Lord Jesus Christ, our God.”

Saint Paphnutius made bold to ask the angel for permission to remain in the desert to the end of his days. The angel replied that God had decreed another path for him. He was to return to Egypt and tell the Christians of the life of the desert-dwellers.

Having bid farewell to the youths, Saint Paphnutius reached the edge of the wilderness after a three day journey. Here he found a small skete, and the brethren received him with love. Abba Paphnutius related everything that he had learned about the holy Fathers whom he had encountered in the desert. The brethren wrote a detailed account of what Saint Paphnutius said, and deposited it in the church, where all who wished to do so could read it. Saint Paphnutius gave thanks to God, Who had granted him to learn about the exalted lives of the hermits of the Thebaid, and he returned to his own monastery.

Saint Theophilus is also commemorated on June 12 with Saint Onuphrius.

Source:

https://oca.org/saints/lives/2016/12/02/103462-st-theophilus-of-egypt