Arbogast (died September 8, 394) was a barbarian general of the Roman Empire, the first to establish a Roman nominee of his own as a puppet emperor and attempt a pagan revival in his name.
Probably of Frankish descent, he rose to the rank of magister equitum (“master of the cavalry”) in the Western Roman army and was sent by the emperor Gratian, in 380, to assist the Eastern ruler Theodosius against the Goths in Thrace. He remained in the service of Theodosius. In 388, after the defeat in Italy of the usurper Magnus Maximus by Theodosius, Arbogast recovered Gaul for the Western emperor Valentinian II from Maximus’s son, Flavius Victor. The following year Arbogast pacified the Rhine frontier, imposing a treaty on the Frankish leaders Marcomer and Sunne, who had invaded Gaul in 384.
By 391 the general had become all-powerful in Gaul as comes (“count”) and regent. When Valentinian attempted to dismiss him, Arbogast tore up the order and declared that only Theodosius possessed the power to do so. On May 15, 392, Valentinian died at Vienna (modern Vienne, France) in circumstances suggestive of murder instigated by Arbogast. Proclaiming Eugenius, a professor of rhetoric, as emperor in the West, Arbogast—who admired the Roman Republic and despised the quarrels between Roman Catholic and Arian Christians—set about restoring paganism. In the winter of 393–394, he conducted a successful campaign against the Ripuarian Franks, the Chamavi, and along the Rhine, but the following May, Theodosius marched west to suppress the pagan revolution. Arbogast attempted to ambush Theodosius, but the two-day battle of Frigidus (at the Frigidus River, modern Vipava River) on September 5 and 6 ended in victory for Theodosius. Eugenius was beheaded; Arbogast committed suicide.