Theophylact was the eldest son of the Byzantine emperor Michael I Rhangabe (r. 811–813) and grandson, on his mother's side, of Nikephoros I (r. 802–811). He was junior co-emperor alongside his father for the duration of the latter's reign and was tonsured, castrated, and exiled to Plate Island after his overthrow, under the monastic name Eustratius.

Theophylact was born to Michael Rhangabe and Prokopia. The couple's oldest child, he was named after his paternal grandfather, the droungarios of the Dodekanesos Theophylact Rhangabe, who had participated in a failed conspiracy to wrest the throne from Empress-regent Irene of Athens in 780. Nevertheless, his maternal grandfather, the emperor Nikephoros I, rose to become General Logothete (finance minister) under Empress Irene before eventually deposing her in October 802.

Depicted here is silver Miliaresion weighing around 2.23g of Constantinople mint. The obverse of a coin depicts the Greek inscription, "Jesus Christ conquers" Cross potent on steps. The reverse of a coin also inscribed with Greek inscription "Michael and Theophylact, emperors of the Romans".

Image Source: https://www.coin.com/