The·o·do·sius I 
(thē′ə-dōshəs, -shē-əs) Known as "Theodosius the Great." AD 346?-395.
(thē′ə-dōshəs, -shē-əs) Known as "Theodosius the Great." AD 346?-395. Emperor of Rome who ruled jointly (379-392) with Gratian and Valentinian II and independently (392-395). He repressed paganism and Arianism and in his will divided the eastern and western portions of the empire between his two sons.