Theodosius I was a Roman emperor who ruled from 379 until his death in 395. Born in Hispania, he rose through the military ranks under his father's guidance before being appointed to lead the empire following the death of Valens. He is notably the final ruler to govern the entire Roman Empire before it was divided between his two sons, Arcadius and Honorius. As a devout Christian, he played a pivotal role in shaping religious policy by establishing the Nicene Creed as the official orthodox doctrine.