From our Synod's website (and also Treasury of Daily Prayer, p. 912):
Justinian was emperor of the East from A.D. 527 to 565 when the Roman Empire was in decline. With his beautiful and capable wife, Theodora, he restored splendor and majesty to the Byzantine court. During his reign the Empire experienced a renaissance, due in large part to his ambition, intelligence, and strong religious convictions. Justinian also attempted to bring unity to a divided church. He was a champion of orthodox Christianity and sought agreement among the parties in the Christological controversies of the day who were disputing the relation between the divine and human natures in the Person of Christ. The Fifth Ecumenical Council in Constantinople in A.D. 533 was held during his reign and addressed this dispute. Justinian died in his eighties, not accomplishing his desire for an empire that was firmly Christian and orthodox.
St. Justinian is credited with a hymn to our Savior that is regularly sung in the Liturgy of St. John Chrysostom:
Only Begotten Son and Immortal Word of God,
Who for our salvation didst will to be incarnate of the holy Theotokos and ever virgin Mary,
Who without change didst become man and wast crucified, O Christ our God,
Trampling down death by death, Who art one of the Holy Trinity,
Glorified with the Father and the Holy Spirit, save us.