Theodosius the Great became the Roman Emperor on 19th January 379. He was the last emperor to rule over the Eastern and the Western halves of the Roman Empire. In 380 Theodosius, I established Christianity as the official religion.
He was born as Flavius Theodosius to a senior military officer Theodosius the Elder around 346. Gratian elevates him at Sirmium to Augustus and gives him authority over all the eastern provinces of the Roman Empire.
Theodosius reformed entire military and coinage system of the Roman Empire. He issued gold and silver coinage minted with his portrait. Represent here is a gold Solidus issued during his reign. The obverse depicts the bust of Theodosius I facing right and inscription DNTHEODO-SIVS P F AVG inscribed on the margin. The reverse of a coin portrays the Constantinopolis, seated facing, head to the right, her right foot set on prow, holding spear with her right hand and placing her left on round shield resting on the column and inscribed VOT / V / MVL / X.
Theodosius I died in 395 due to dropsy. After his death, Theodosius' sons Arcadius and Honorius inherited the East and West halves respectively, and the Roman Empire was never again re-united.
Image Source: coinarchives.com