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Theophylact was born to Michael Rhangabe and Prokopia . He was the couple's oldest child, but the list of his siblings given in the hagiography of Patriarch Ignatius I of Constantinople, who was Theophylact's youngest brother, is unclear on whether he was the eldest child or was born after his oldest sister Gorgo. 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.