Final answer:
Justin was the uncle of Justinian I, who used his influence to change the laws so he could marry Theodora. Theodora emerged as a co-ruler beside Justinian, significantly affecting law reforms, architectural projects, and military campaigns.
Step-by-step explanation:
Justin was the uncle and predecessor of Justinian I, the Eastern Roman Emperor from 527 to 565. Justinian's relationship to Justin was that of a nephew to an uncle. Initially, as a man of senatorial rank, Justinian was prohibited by ancient laws from marrying a courtesan like Theodora. However, Justinian compelled Justin I to enact a new law allowing him to marry her. This action demonstrated the influence and power Justinian wielded even before he assumed the imperial office.
As an empress, Theodora was exceptionally powerful and influential, acting as a co-ruler with Justinian. Despite her controversial past, likely exaggerated by historians like Procopius, Theodora played a significant role in shaping legal reforms and supporting Justinian's ambitions, including his architectural projects like the Hagia Sophia and military campaigns against the Persians and in Italy.