Constantius III (421, seven months) - Western Emperor. The power behind the throne for most of the 410s, he was co-emperor for seven months with Honorius. He died of natural causes whilst in the middle of working on a military expedition to have his rights recognised by his eastern colleague Theodosius II. 

Joannes (423-5) - Western Emperor. A pretender vs. Valentinian III, he was proclaimed emperor at Rome, and had a very shadowy reign. According to Procopius, when captured by the forces of the Eastern empire, first his hand was cut off, and he was then paraded on a donkey in the hippodrome of Aquileia before being beheaded.

Valentinian III (424-455) - Western Emperor. Became emperor in his infancy, ruling under the regency of his mother Galla Placidia, who was fully supported by Theodosius II. He ruled in his own right from 437, but really was under the control of the general Aëtius. During his reign, the Roman empire was raged across by Attila the Hun, something which was only truly ended by Attila's death and the subsequent power struggle between his sons. After Aëtius' assassination at Valentinian's hands (egged on by Petronius Maximus, who we'll get to soon!), he himself was shortly assassinated by Aëtius' followers... possibly, again, egged on by Petronius Maximus, who seems to have been a bit of a chess player. 

Constantius III, a member of a noble Roman family, he became master of the soldiers under the emperor of the West, Honorius.

Constantius distinguished himself in 411 and the years following by overcoming various usurpers in Gaul and forcing the Visigoths to evacuate that region and move on to Spain. The Visigoths also surrendered Galla Placidia, Honorius' sister, whom they had carried off from the sack of Rome in 410.