Justinian I was a Roman emperor who reigned from 527 to 565 CE during the late antique period. Born in 482 CE in a Latin-speaking province, he was brought to Constantinople by his uncle, Emperor Justin I, whom he succeeded. His reign was defined by major military campaigns to reclaim lost western territories, vast construction projects, and profound legal and religious reforms. He ruled alongside his influential wife, Theodora, and his time in power faced significant challenges including major riots, a devastating plague, and continuous wars.

Although an emperor, his direct involvement in scholarly and legal projects means he is also significant for his theological and legislative works. Under his authority, a comprehensive codification of Roman law, known as the Corpus Juris Civilis, was produced. This included the Codex Justinianus, the Digesta, the Institutiones, and later laws called the Novellae. He also authored or sponsored numerous theological edicts and treatises aimed at defining orthodox Christian doctrine.

His historical importance is immense and dual-natured. According to modern scholars, his legal codification preserved Roman law and became the foundational text for most European civil law systems. In religious matters, he aggressively enforced doctrinal unity, which included persecuting non-Christians and certain Christian groups, and he convened the Fifth Ecumenical Council in 553 CE. His ambitious military campaigns temporarily restored Roman control in the West but strained the empire's resources. Furthermore, his architectural legacy, most famously the Hagia Sophia in Constantinople, left a permanent mark on Byzantine and Orthodox Christian culture.