Constantius III - Augustus of Imperium Romanum (West) from February 8, 421 AD to 2 September 421 AD
Flavius Constantius Augustus as Western Roman Emperor for seven months in 421. A prominent general and politician, he was the power behind the throne for much of the 410s, and in 421 briefly became co-emperor of the Western Empire with Honorius.

He married the sister of Honorius & Arcadius - Galla Placidia - and had two children with her, and on the 8th of February 421 AD he was proclaimed co-emperor to his useless brother-in-law, Honorius.

He was organizing a military expedition to the East to have his rights recognized when he died suddenly on September 2, 421. His son would eventually rule as Valentinian III.
Constantius III
Emperor Constantius III of the Roman Empire (West)