Justin I, c.450–527, Byzantine emperor (518–27); successor of Anastasius I. He was chief of the imperial guard and became emperor when Anastasius died. Justin persecuted the Monophysites and maintained close relations with the Western Church. An uneducated man, he entrusted the government largely to his nephew, who eventually succeeded him as Justinian I.
See A. Vasiliev, Justin the First (1950).