Arbogast (Arbogastes), a Gaul in the military service of the Romans during the latter half of the 4th century. In 388 he accompanied Theodosius on his expedition to support Valentinian II. against the usurper Maximus. After the revolt was reduced, Arbogast, by the order of Theodosius, remained with Valentinian as adviser; and when the latter attempted to recover his independence, Arbogast put to death all his partisans, and finally the emperor himself. Not daring to seize upon the imperial purple, he gave it to Eugenius, going himself to light against Marcomir, chief of the Franks. Theodosius marched into Italy to avenge his cousin, and Arbogast and Eugenius were defeated in the passes of the Julian Alps, in 394. Eugenius was captured and executed. Arbogast escaped into the mountains, but soon despairing, committed suicide.