Nicephorus I, d. 811, Byzantine emperor (802–11). He was minister of finance under Empress Irene, whom he deposed and succeeded. He improved the treasury, revised taxation, and vigorously asserted imperial authority over the church. This policy and his appointment of St. Nicephorus to the patriarchate of Constantinople precipitated a conflict with Theodore of Studium, whom he exiled in 809. Nicephorus consolidated Byzantine strength in the Balkans. He was killed while fighting the Bulgars and was succeeded briefly by his son Stauracius and then by his son-in-law, Michael I.