Known as Hilarion the Younger, Hilarion 1 was hegoumenos of the monastery of Dalmatos at Constantinople and an archimandrite and his Life was composed soon after his death (in 845, see below) by a monk called Sabas: Vita Hilarionis Dalmat. (= Codex Vaticanus graecus 984; see Costa-Louillet, in Byz 25-27 (1955-1957), pp. 788ff.) title: Βίος ἤτοι πολιτεία τοῦ ὁσίου πατρὸς ἡμῶν καὶ ἀρχιμανδρίτου Ἱλαρίωνος ἡγουμένου μονῆς τῶν Δαλμάτου, cf. Synax. Eccl. Const. 731-734, Vita Hilarionis, AASS June I, 746-748.

He was born in 775 (see below), the son of Petros 130 of Cappadocia and Theodosia 3 and the brother of Agapios 5; at the age of twenty-five he left his parents, renounced his worldly wealth and entered the monastery of Xerokepos at Constantinople; later he transferred to the monastery of Dalmatos, where he received the dress of a monk; he remained at the monastery of Dalmatos for ten years, working there as a gardener, although in his youth he had studied letters; in 806 he was ordained as priest by his hegoumenos (Anonymus 676) but when Anonymus 676 died soon afterwards Hilarion 1 left the monastery and visited the Opsikion thema where he took refuge in the monastery of Kathara, remaining there in 806 and 807; the monks of Dalmatos wanted him as their next hegoumenos and he eventually submitted, though only after the patriarch Nikephoros 2 and then the emperor Nikephoros 8 had summoned him to do so; he then became hegoumenos of the monastery of Dalmatos and archimandrite of the monasteries in Constantinople (in 807); he ruled the monastery from 807 until 815; during the persecution under Leo V (Leo 15) he refused to abandon icons; he was several times interviewed by the emperor but refused to give way and spent the intervening periods in various prisons; at one point he was kept in a small cell by the patriarch (most probably Theodotos 2 Kassiteras) and subjected to starvation; later he was held in the monastery Tou Phoneos for six months and afterwards, after again refusing to give way, was sent for over two years to the monastery of Kyklobion, then to the Noumera prison where he was flogged and finally to the stronghold of Protilion; he was there when Michael II (Michael 10) became emperor and under him was released; he then lodged in the house of a pious lady, probably in Constantinople, for seven years, which passed peacefully; during the reign of Theophilos 5 he again refused to abandon icons and made accusations against the emperor; he was again beaten and was sent into exile at Aphousia, to the south of Prokonnesos, where he spent eight years in a narrow cell and where he performed a number of miracles; after the death of Theophilos 5 he was recalled under Theodora 2 and returned to the monastery of Dalmatos where he performed more miracles; he lived for three more years (842-845) and then died at the age of seventy, in 845: Vita Hilarionis Dalmat., pp. 17-29, Synax. Eccl. Const. 731-734, Vita Hilarionis, AASS June I, 746-748. The date of his death was either 6 June, Vita Hilarionis, AASS June I, 746, Synax. Eccl. Const. 731; or 10 June, Codex Vaticanus graecus 984. An archimandrite, addressee of a letter from Theodore the Stoudite (Theodoros 15), written in 816, in which Theodoros 15 enquired about his fate during the current persecution; he is styled σου ἡ τιμιότης (p. 211, line 3) and τῆς πατρότητός σου (p. 211, line 6) and addressed as ὦ πάτερ (p. 211, line 10): Theod. Stud., Ep. 90, p. 211 (addressed Ἱλαρίωνι ἀρχιμανδρίτῃ). He is also mentioned in three other letters of Theodoros 15, written between 816 and 818, and in a sermon in the Catechesis Magna: Theod. Stud., Epp. 214, pp. 336-337 (?a. 816); 267, pp. 394-395 (L 816/E 817); 291, p. 430 (February 818), Catech. Magna 89 (p. 631 Papadopoulos-Kerameus) (dedicated to him; Theodoros 15 played a role in his selection as hegoumenos). During the persecution under Leo V (Leo 15) he was apparently in the company of Theophanes 18 in 816, and possibly in 818 (Theodoros 15 was not sure if they were still together, Ep. 291, p. 430, and cf. also Pargoire, VV 9, pp. 84ff.); Theodoros 15 refers to him as ὁ ἔξαρχος: Theod. Stud., Epp. 214 (τὸν σύναθλόν σου, πατέρα δὲ ἐμόν, φημὶ τὸν ἔξαρχον: p. 337, lines 20-21), 291 (ὁ πατήρ μου καὶ ἔξαρχος: p. 430, line 20). Referred to, but not named, as the hegoumenos of the Dalmatos monastery (in late 816/early 817): Theod. Stud., Ep. 267 (ὁ τῆς Δελμάτου, sc. ἡγούμενος: p. 395, lines 30-31).

Hegoumenos of the monastery of Dalmatos at Constantinople, described as a holy man and a confessor (ὁ ὅσιος καὶ ὁμολογητὴς Ἱλαρίων ὁ τῆς Δαλμάτου sc. μονῆς ἡγούμενος); he allegedly told Eirene 6 (the mother of Photios 1), before his birth, that the child she was carrying was Satan incarnate: Ps.-Symeon 669. The story is part of an account which is very hostile to Photios 1, and was probably a later malicious invention. See further Beck, Kirche, p. 558. His Vita (unpublished, BHG 2177) is in Codex Vaticanus graecus 984, ff. 203v-206; see AASS June I 759-760 (= Synax. Eccl. Const. 731-734), and now see Matantseva, RSBN, n.s. 30 (1993), pp. 17-29 and cf. PmbZ, Prolegomena, 62-63, and PmbZ 2584.

Styled τοῦ ὁσιωτάτου ἀρχιμανδρίτου καὶ ἡγουμένου τῶν Δαλμάτου, he is included among those acclaimed for their support of icons in the Synodikon of Orthodoxy: Gouillard, "Synodikon", p. 53, line 130.

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