497--d. June 28, 548, Constantinople, Byzantine empress, wife of the emperor Justinian I (reigned 527-565), probably the most powerful woman in Byzantine history. Her intelligence and political acumen made her Justinian's most trusted adviser and enabled her to use the power and influence of her office to promote religious and social policies that favoured her interests.

Little is known of Theodora's early life, but a combination of the official version with that found in the highly coloured Secret History of Procopius of Caesarea probably provides the best explanation. Her father was a bear keeper at the Hippodrome (circus) in Constantinople. She became an actress while still young, leading an unconventional life that included giving birth to at least one child out of wedlock. For a time, she made her living as a wool spinner. When Justinian met her, she had been converted to monophysitism, a non-orthodox doctrine. Attracted by her beauty and intelligence, he made her his mistress, raised her to the rank of patrician, and in 525 married her. When Justinian succeeded to the throne in 527, she was proclaimed augusta.

Theodora exercised considerable influence, and though she was never coregent, her superior intelligence and deft handling of political affairs caused many to think that it was she, rather than Justinian, who ruled Byzantium. Her name is mentioned in nearly all the laws passed during that period. She received foreign envoys and corresponded with foreign rulers, functions usually reserved for the emperor. Her influence in political affairs was decisive, as illustrated in the Nika revolt of January 532. The two political factions in Constantinople, the Blues and the Greens, united in their opposition to the government and set up a rival emperor. Justinian's advisers urged him to flee, but Theodora advised him to stay and save his empire, whereupon Justinian's general, Belisarius, herded the rioters into the Hippodrome and cut them to pieces.

Theodora is remembered as one of the first rulers to recognize the rights of women, passing strict laws to prohibit the traffic in young girls and altering the divorce laws to give greater benefits to women. She spent much of her reign trying to mitigate the laws against the monophysites. Though she succeeded in ending their persecution in 533, she never succeeded in changing Justinian's religious policy from its emphasis on orthodoxy and friendship with Rome.

The best-known representation of Theodora is the mosaic portrait in the Church of San Vitale in Ravenna. Her death, possibly from cancer or gangrene, was a severe blow to Justinian. Her importance in Byzantine political life is shown by the fact that little significant legislation dates from the period between her death and that of Justinian (565).