Nikephoros 21 was founder of the monastery of Medikion in Bithynia and was its hegoumenos from before 787 to his death in 813. Hegoumenos of the monastery of Hagios Sergios of Medikion; in 787 he attended the Second Council of Nikaia (the Seventh Ecumenical Council) and is attested at the fourth session, on 1 October 787, when he subscribed the statements read out from the Fathers in support of the veneration of icons: Mansi XIII 153 (Νικηφόρος ἡγούμενος τοῦ ἁγίου Σεργίου τοῦ Μιδικιῶνος; the Latin version, at XIII 154, calls him "hegumenus sancti Sergii Midicionis"). On the monastery of Medikion near Prousa, cf. Ramsay, Historical Geography, p. 180. He probably attended other sessions of the Council also; see Gregorios 45. He was the founder of the monastery of Medikion and was its hegoumenos and it was he who welcomed Niketas of Medikion (Niketas 43) there (ὑπὸ τοῦ ὁσιωτάτου πατρὸς ἡμῶν τοῦ ταύτην συστησαμένου διεπομένην Νικηφόρου): Vita Nicetae Medicii (AASS April I) 8. Some five years later Nikephoros 21 sent Niketas 43 to Constantinople to be ordained priest by Tarasios 1 and on Niketas 43's return entrusted him with the management of the monastery (τὴν φροντίδα τῆς μονῆς): Vita Nicetae Medicii 10. Nikephoros 21 died on 4 May 813: Vita Nicetae Medicii 24. Cf. also Athanasios 5.

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