Final answer:
Justinian I was the Byzantine emperor who sought to restore the Roman Empire's former glory by expanding its territory and enforcing religious uniformity.
Step-by-step explanation:
The Byzantine emperor who sought to restore the greatness of the Roman Empire was Justinian I. His reign from 527 to 565 saw the Byzantine Empire reach its greatest extent, with lands encompassing the Balkans, Egypt, north Africa, Anatolia, the Levant, Italy, and the southern Iberian Peninsula. Justinian's notable military campaigns included the reconquest of Italy from the Ostrogoths and North Africa from the Vandals. His reign is also remembered for significant architectural achievements like the construction of the Hagia Sophia and for attempting to enforce religious uniformity in Christianity.
Despite later territorial losses in Europe, the Byzantine Empire maintained more coherent and defensible borders, securing regions such as Anatolia under Emperor Leo the Isaurian. Justinian I endeavored to link his rule with the divinity by adopting the title "beloved of Christ" and imposing Christian orthodoxy to counter heresy.