Ioannes 438 was hegoumenos of the monastery of Antidios, on Mt Olympus in Bithynia, in the late eighth century and the early ninth. He welcomed Ioannikios 2 at his monastery shortly after Ioannikios 2 decided to withdraw from the world; Ioannikios 2 spent two years at the monastery of Antidios acquiring the basic knowledge to become a monk: Sabas, Vita Ioannicii 9 (ὁ πατὴρ τῆς μονῆς ἐκείνης, Ἰωάννης προσαγορευόμενος), Petrus, Vita Ioannicii 9 (τὸν τῆς μονῆς προεστῶτα - unnamed). Ioannes 438 gave Ioannikios 2 his blessing when two years later Ioannikios 2 left to return to the monastery of Agauroi: Sabas, Vita Ioannicii 10. He was apparently still hegoumenos some years later when Ioannikios 2 returned from Mt Alsos in Lydia after visiting Georgios 220 and returned via Antidios to Agauroi: Sabas, Vita Ioannicii 14 (πρὸς τὸν τῆς Ἀντιδίου μονῆς ποιμένα Ἰωάννην).

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