Leo I (Latin: Flavius Valerius Leo Augustus; 401 – 18 January 474) was Eastern Roman Emperor from 457 to 474.
A native of Dacia Aureliana near historic Thrace, he was known as Leo the Thracian (Greek: ???? ?' ? T??? Leon ho Thrax).
Ruling the Eastern Empire for nearly 20 years, Leo proved to be a capable ruler.
He oversaw many ambitious political and military plans, aimed mostly at aiding the faltering Western Roman Empire and recovering its former territories.
He is notable for being the first Eastern Emperor to legislate in Koine Greek rather than Late Latin.He is commemorated as a Saint in the Orthodox Church, with his feast day on January 20.