Valentinian II, 371?–392, Roman emperor of the West (375–92), son of Valentinian I. Upon the death of his father, he was proclaimed emperor with his brother Gratian as coregent. After the death (378) of Valens, Gratian made Theodosius I ruler in the East. Valentinian's reign during his minority was troubled by the religious struggle between the Arians, supported by his mother, Justina, and the Nicene Christians led by Gratian and St. Ambrose. In 383, Gratian was killed by order of Maximus, and the personal rule of Valentinian began. He was expelled (387) from Italy by Maximus but was restored by Theodosius in 388. Valentinian was murdered four years later, perhaps by the Frankish general Arbogast, who then named the puppet Eugenius as emperor.