<P> Honorius became Western Emperor in 395, after the death of his father Theodosius . His reign was beset by barbarian invasions, and for much of his early reign, until 408, he was controlled by Stilicho, whose influence over Honorius would create a standard for puppet Western Emperors . Honorius died of edema in 423 . </P> <Ul> <Li> Valentinian III: 425--455 . </Li> </Ul> <Li> Valentinian III: 425--455 . </Li> <P> Valentinian III was designated Honorius' heir in 421, although he was not proclaimed caesar, only given the title of nobilissimus puer . In 423, after the death of Honorius, a usurper named Joannes rose up, forcing Valentinian III to flee with his family to the court of the Eastern Emperor Theodosius II . He was installed as Western Emperor in 425, after Joannes was defeated by Theodosius in Ravenna . Valentinian was killed on 16 March 455, by Optila, a friend of Flavius Aetius, whom Valentinian had killed . </P>

Who ruled their respective halves of the roman empire