Justinian I ( /dʒʌˈstɪniən/) (Latin: Flavius Petrus Sabbatius Iustinianus Augustus, Ancient Greek: Φλάβιος Πέτρος Σαββάτιος Ἰουστινιανός) (c. 482 – 14 November 565), commonly known as Justinian the Great, was Byzantine Emperor from 527 to 565. During his reign, Justinian sought to revive the Empire's greatness and reconquer the lost western half of the classical Roman Empire.

One of the most important figures of Late Antiquity and the last Roman Emperor to speak Latin as a first language, Justinian's rule constitutes a distinct epoch in the history of the Eastern Roman Empire. The impact of his administration extended far beyond the boundaries of his time and domain. Justinian's reign is marked by the ambitious but only partly realized renovatio imperii, or "restoration of the Empire". This ambition was expressed by the partial recovery of the territories of the defunct Western Roman Empire. His general Belisarius swiftly conquered the Vandal Kingdom in North Africa, extending Roman control to the Atlantic Ocean. Subsequently Belisarius, Narses, and other generals conquered the Ostrogothic Kingdom, restoring Dalmatia, Sicily, Italy, and Rome to the Empire after more than half a century of barbarian control.