We gather from his writings (the only remaining being his apology to Autolycus) that he was born a pagan, not far from the Tigris and Euphrates, and was led to embrace Christianity by studying the Holy Scriptures, especially the prophetical books. He makes no reference to his office in his existing writings, nor is any other fact in his life recorded. Eusebius, however, speaks of the zeal which he and the other chief shepherds displayed in driving away the heretics who were attacking Christ's flock, with special mention of his work against Marcion. He made contributions to the departments of Christian literature, polemics, exegetics, and apologetics. William Sanday describes him as "one of the precursors of that group of writers who, from Irenaeus to Cyprian, not only break the obscurity which rests on the earliest history of the Christian church, but alike in the East and in the West carry it to the front in literary eminence, and distance all their heathen contemporaries".
Eusebius and Jerome mention numerous works of Theophilus existing in their time. They are:
Theophilus's critical powers were not above his age. He adopts Herodotus's derivation (ii. 52) of qeus from tiqhmi, since God set all things in order, comparing with it that of Plato (Cratylus 397C) from qeein, because the Deity is ever in motion (Apologia i. 4). He asserts that Satan is called the dragon (Greek drakon) on account of his having revolted apodedrakenai from God (ii. 28), and traces the Bacchanalian cry "Evoe" to the name of Eve as the first sinner (ibid.). His physical theories are equally embarrassing. He ridicules those who maintain the spherical form of the earth (ii. 32) and asserts that it is a flat surface covered by the heavens as by a domical vault (ii. 13). His exegesis is based on allegories usually of the most arbitrary character. He makes no attempt to determine the real meaning of a passage, but seeks to find some recondite spiritual truth, a method which often leads him to great absurdities. He discovers the reason of blood coagulating on the surface of the ground in the divine word to Cain (Genesis 4:10-12), the earth struck with terror refusing to drink it in.
Theophilus's testimony to the Old Testament is copious. He quotes very largely from the Pentateuch and to a smaller extent from the other historical books. His references to Psalms, Proverbs, Isaiah, and Jeremiah are copious, and he quotes from Ezekiel, Hosea and other minor prophets. His direct evidence respecting the canon of the New Testament does not go much beyond a few precepts from the Sermon on the Mount (iii. 13, 14), a possible quotation from Luke 18:27 (ii. 13), and quotations from Romans, 1 Corinthians, and 1 Timothy. More important is a distinct citation from the opening of the Gospel of St. John (1:1-3), mentioning the evangelist by name, as one of the inspired men by whom the Holy Scriptures were written (ii. 22). The use of a metaphor found in 2 Peter 1:19 bears on the date of that epistle. According to Eusebius, Theophilus quoted the Book of Revelation in his work against Hermogenes; a very precarious allusion has been seen in ii. 28, cf. Revelation 12:3, 7, etc. A full index of these and other possible references to the Old and New Testament is given by Otto (Corp. Apol. Christ. ii. 353-355). Theophilus transcribes a considerable portion of Genesis chapters 1-3 with his own allegorizing comments upon the successive work of the creation week. The sun is the image of God; the moon of man, whose death and resurrection are prefigured by the monthly changes of that luminary. The first three days before the creation of the heavenly bodies are types of the Trinity -- the first place in Christian writings where that terminology is known to occur (ii. 15): i.e. "God, His Word and His Wisdom."
The silence regarding his Apology in the East is remarkable; we fail to find the work mentioned or quoted by Greek writers before the time of Eusebius. Several passages in the works of Irenaeus show an undoubted relationship to passages in one small section of the Apologia (Iren. v. 23, 1; Autol. ii. 25 init.: Iren. iv. 38, 1, iii. 23, 6; Autol. ii. 25: Iren. iii. 23, 6; Autol. ii. 25, 26), but Harnack thinks it probable that the quotations, limited to two chapters, are not taken from the Apologia, but from Theophilus's work against Marcion (cf. Möhler, Patr. p. 286; Otto, Corp. Apol. II. viii. p. 357; Donaldson, History of Christian Literature iii, 66). In the West there are a few references to the Autolycus. It is quoted by Lactantius (Div. Inst. i. 23) under the title Liber de Temporibus ad Autolycum. There is a passage first cited by Maranus in Novatian (de Trin. c. 2) which shows great similarity to the language of Theophilus (ad Autol. i. 3). In the next century the book is mentioned by Gennadius (c. 34) as "tres libelli de fide." He found them attributed to Theophilus of Alexandria, but the disparity of style caused him to question the authorship. The notice of Theophilus by Jerome has been already referred to. Henry Dodwell found internal evidence, in the reference to existing persecutions and a supposed reference to Origen and his followers, for assigning the work to a younger Theophilus who perished in the reign of Septimius Severus. His arguments have been carefully examined by Tillemont (Mém. eccl. iii. 612 notes), William Cave, Donaldson, and Harnack, and the received authorship fully established. Compare W. Sanday in Stud. Bibl. (Oxford, 1885), p. 89.