Tatian the heresiarch.

One of the Christian apologists, deemed heretical and apostate.

Attributed text(s).
Address to the Greeks.
The Diatessaron.
Concerning Perfection.

Available text(s).
Skeptik (To the Greeks, Greek only).
CCEL: To the Greeks (English only).
Early Christian Writings: To the Greeks and the Diatessaron (English only).
New Advent: The Diatessaron (English only).

Related text(s).
The Dura-Europos fragment.

Useful links.
Tatian at EarlyChurch.
Tatian in the Catholic Encyclopedia.
Tatian and the Diatessaron at Early Christian Writings.

Tatian was a Christian apologist who flourished late in century II and founded the encratites.

From Irenaeus, Against Heresies 1.28.1 (translation modified slightly from that of the Ante-Nicene Fathers series):

Ut exempli gratia dicamus, a Saturnino et Marcione, qui vocantur continentes, abstinentiam a nuptiis annuntiaverunt, frustrantes antiquam plasmationem dei, et oblique accusantes eum qui et masculum et foeminam ad generationem hominum fecit; et corum quae dicuntur apud eos animalia abstinentiam induxerunt, ingrati exsistentes ei qui omnia fecit deo. contradicunt quoque eius saluti, qui primus plasmatus est, et hoc nunc adinventum est apud eos. Tatiano quodam primo hanc introducente blasphemiam, qui cum esset Iustini auditor, in quantum quidem apud eum erat, nihil enarravit tale; post vero illius martyrium absistens ab ecclesia, et praesumptione magistri elatus et inflatus, quasi prae caeteris esset, proprium characterem doctrinae constituit. aeonas quosdam invisibiles similiter atque hi qui a Valentino sunt, velut fabulam enarrans; nuptias autem corruptelas et fornicationes similiter ut Marcion et Saturninus dicens; Adae autem saluti ex se contradictionem faciens.

To give an example: Springing from Saturninus and Marcion, those who are called continent ones, preached against marriage, thus setting aside the original creation of God, and indirectly blaming him who made the male and female for the propagation of the human race. Some of those reckoned among them have also introduced abstinence from animal food, thus proving themselves ungrateful to God, who formed all things. They deny, too, the salvation of him who was first created. It is but lately, however, that this opinion has been invented among them. A certain man named Tatian first introduced the blasphemy. He was a hearer of Justin, and as long as he continued with him he expressed no such views; but after his martyrdom he separated from the church, and, excited and puffed up by the thought of being a teacher, as if he were superior to others, he composed his own peculiar type of doctrine. He invented a system of certain invisible aeons, like the followers of Valentinus, while, like Marcion and Saturninus, he declared that marriage was nothing else than corruption and fornication. But his denial of the salvation of Adam was an opinion due entirely to himself.

Eusebius provides the original Greek of this passage in History of the Church 4.29.2-3 (see below).

Eusebius writes in History of the Church 4.28[.1] (translation modified slightly from that of the Ante-Nicene Fathers series):

Και Μουσανου δε, ον εν τοις φθασασιν κατελεξαμεν, φερεται τις επιστρεπτικωτατος λογος, προς τινας αυτω γραφεις αδελφους αποκλιναντας επι την των λεγομενων εγκρατιτων αιρεσιν, αρτι τοτε φυειν αρχομενην ξενην τε και φθοριμαιαν ψευδοδοξιαν εισαγουσαν τω βιω.

And of Musanus also, whom we have listed among the foregoing, there is extant a certain very elegant volume, written by him against certain brethren that had turned over to the heresy of the so-called encratites, which had almost at that time begun to flourish and brought to life a strange and pernicious false doctrine.

He continues immediately in 4.29.1-7:

Ης παρεκτροπης αρχηγον καταστηναι Τατιανον λογος εχει, ου μικρω προσθεν τας περι του θαυμασιου Ιουστινου παρατεθειμεθα λεξεις, μαθητην αυτον ιστορουντες του μαρτυρος. δηλοι δε τουτο Ειρηναιος εν τω πρωτω των προς τας αιρεσεις, ομου τα τε περι αυτου και της κατ αυτον αιρεσεως ουτω γραφων·

The word is that Tatian was the author of this [false doctrine], whose words we quoted a little before concerning the marvelous Justin, and whom we recorded to have been a disciple of the martyr. And Irenaeus declares this in the first of his [volumes] against the heresies, where he writes thus concerning both him and his heresy:

Απο Σατορνινου και Μαρκιωνος οι καλουμενοι εγκρατεις αγαμιαν εκηρυξαν, αθετουντες την αρχαιαν πλασιν του θεου και ηρεμα κατηγορουντες του αρρεν και θηλυ εις γενεσιν ανθρωπων πεποιηκοτος, και των λεγομενων παρ αυτοις εμψυχων αποχην εισηγησαντο, αχαριστουντες τω παντα πεποιηκοτι θεω, αντιλεγουσι τε τη του πρωτοπλαστου σωτηρια. και τουτο νυν εξευρεθη παρ αυτοις Τατιανου τινος πρωτως ταυτην εισενεγκαντος την βλασφημιαν· ος Ιουστινου ακροατης γεγονως, εφ οσον μεν συνην εκεινω, ουδεν εξεφηνεν τοιουτον, μετα δε την εκεινου μαρτυριαν αποστας της εκκλησιας, οιηματι διδασκαλου επαρθεις και τυφωθεις ως διαφερων των λοιπων, ιδιον χαρακτηρα διδασκαλειου συνεστησατο, αιωνας τινας αορατους ομοιως τοις απο 0υαλεντινου μυθολογησας γαμον τε φθοραν και πορνειαν παραπλησιως Μαρκιωνι και Σατορνινω αναγορευσας, τη δε του Αδαμ σωτηρια παρ εαυτου την αντιλογιαν ποιησαμενος.

Those who are called encratites, and who sprang from Saturninus and Marcion, preached celibacy, setting aside the original arrangement of God and tacitly censuring him who made male and female for the propagation of the human race. They introduced also abstinence from the things called by them animate, thus showing ingratitude to the God who made all things. And they deny the salvation of the first man. But this has been only recently discovered by them, a certain Tatian being the first to introduce this blasphemy. He was a hearer of Justin, and expressed no such opinion while he was with him, but after the martyrdom of the latter he left the church, and, becoming exalted with the thought of being a teacher and puffed up with the idea that he was superior to others, he established a peculiar type of doctrine of his own, inventing certain invisible aeons like the followers of Valentinus, while, like Marcion and Saturninus, he pronounced marriage to be corruption and fornication. His argument against the salvation of Adam, however, he devised for himself.

Ταυτα μεν ο Ειρηναιος τοτε.

Irenaeus wrote these things at that time.

Σμικρω δε υστερον Σευηρος τις τουνομα κρατυνας την προδεδηλωμενην αιρεσιν, αιτιος τοις εξ αυτης ωρμημενοις της απ αυτου παρηγμενης Σευηριανων προσηγοριας γεγονεν.

But a little later a certain man named Severus put new strength into the aforesaid heresy, and thus brought it about that those who took their origin from it were called, after him, Severians.

Χρωνται μεν ουν ουτοι νομω και προφηταις και ευαγγελιοις, ιδιως ερμηνευοντες των ιερων τα νοηματα γραφων· βλασφημουντες δε Παυλον τον αποστολον, αθετουσιν αυτου τας επιστολας, μηδε τας πραξεις των αποστολων καταδεχομενοι.

They, indeed, use the law and prophets and gospels, but interpret in their own way the utterances of the sacred scriptures. And they abuse Paul the apostle and reject his epistles, and do not accept even the Acts of the Apostles.

Ο μεντοι γε προτερος αυτων αρχηγος ο Τατιανος συναφειαν τινα και συναγωγην, ουκ οιδ οπως, των ευαγγελιων συνθεις το δια τεσσαρων τουτο προσωνομασεν, ο και παρα τισιν εις ετι νυν φερεται· του δ αποστολου φασι τολμησαι τινας αυτον μεταφρασαι φωνας, ως επιδιορθουμενον αυτων την της φρασεως συνταξιν.

At any rate, their former leader, Tatian, put together a certain combination and collection of the gospels, I do not know how, and named it the Diatessaron, which is still even now extant for some. But they say that he dared to paraphrase certain words of the apostle, as correcting the syntax of their phrasing.

Καταλελοιπεν δε ουτος πολυ τι πληθος συγγραμματων, ων μαλιστα παρα πολλοις μνημονευεται διαβοητος αυτου λογος ο προς Ελληνας, εν ω και των ανεκαθεν χρονων μνημονευσας, των παρ Ελλησιν ευδοκιμων απαντων προγενεστερον Μωυσεα τε και τους Εβραιων προφητας απεφηνεν· ος δη και δοκει των συγγραμματων απαντων αυτου καλλιστος τε και ωφελιμωτατος υπαρχειν. και τα μεν κατα τουσδε τοιαυτα ην.

He has left a great many writings. Of these the one most in use among many persons is his celebrated address to the Greeks, which also appears to be the best and most useful of all his works. In it he deals with the most ancient times, and shows that Moses and the Hebrew prophets were older than all the celebrated men among the Greeks. So much in regard to these men.

Jerome, On Famous Men 29:

Tatianus, qui primum oratoriam docens non parvam sibi ex arte rhetorica gloriam comparaverat, Iustini martyris sectator fuit, florens in ecclesia quamdiu ab eius latere non discessit. postea vero inflatus eloquentiae tumore, novam condidit haeresim quae εγκρατιτων dicitur, quam postea Severus auxit, a quo eiusdem partis haeretici Severiani usque hodie appellantur. porro Tatianus infinita scripsit volumina, e quibus unus contra gentes florentissimus exstat liber, qui inter omnia opera eius fertur insignis. et hic sub imperatore M. Antonino Vero et L. Aurelio Commodo floruit.

Tatian, who while at first teaching oratory bought not a little glory for himself from his rhetorical art, was a follower of Justin the martyr, flourishing in the church so long as he did not depart from his side. Afterward, however, inflated by a swelling of eloquence, he founded a new heresy which is called that of the encratites, which Severus afterward augmented, from which heretics of this same party are named Severians even until today. Tatian wrote besides infinite volumes, one of which is extant against the gentiles,* a most successful book, which is deemed to be the most significant among all his works. And he flourished under the emperor Marcus Antoninus Verus and Lucius Aurelius Commodus.

* Literally, against the races.

Jerome, preface to his commentary on Titus, on the Pauline epistles:

Sed Tatianus, qui et ipse nonnullas Pauli epistolas repudiavit, hanc vel maxime, h[oc] e[st], ad Titum, apostoli pronuntiandam credidit; parvipendens Marcionis et aliorum, qui cum eo in hac parte consentiunt, assertionem.

But Tatian, who also himself repudiated certain epistles of Paul, believed that this one in particular, that is, [the one] to Titus, was to be acknowledged as belonging to the apostle, slighting the assertion of Marcion and others, who agree with him in this matter [of rejecting Pauline epistles].