Valentinian III, 419–55, Roman emperor of the West (425–55). Two years after the death of his uncle, Honorius, he was placed on the throne by his cousin Theodosius II, who deposed the usurper John. Valentinian's mother, Galla Placidia, was regent during his minority, but from 433 to 454 the general Aetius was the actual ruler in the West. In Africa, Boniface was defeated (430) by the Vandals under Gaiseric; by 442 Aetius was obliged to acknowledge Vandal independence. The empire was also disturbed by the war between Aetius and Boniface, by general barbarian unrest, and by peasant revolts. Valentinian proved an indolent and ineffectual ruler, although he supported the efforts of Pope Leo I (see Leo I, Saint) to enforce ecclesiastical order in the West. The terrible invasions of the Huns under Attila began in 441; although defeated (451) in Gaul by Aetius, Attila briefly invaded N Italy in 452. In 454, Valentinian murdered Aetius, and shortly afterward Valentinian was himself assassinated. He was succeeded by Maximus.