John I (John Tzimisces) (tsimis'ēz) [key], c.925–976, Byzantine emperor (969–76). With the aid of Emperor Nicephorus II's wife, Theophano, John had Nicephorus murdered and himself proclaimed emperor. John gained the favor of the patriarch of Constantinople by revoking his predecessor's anticlerical legislation. He regained E Bulgaria from the Russians and extended Byzantine power in Syria at the expense of the Muslims. He was succeeded by Basil II.
