Valens was co-emperor with his brother Valentian I (and later co-emperor with other members of the Theodosian Dynasty). Emperor of the East from 364, his reign was constant battle against the Persians and the Goths. He was killed at or immediately after the Battle of Adrianople against the Goths in 378.
The victorious Gothic horsemen now wheeled inward, attacking the flanks and rear of the Roman infantry. At that moment, the Gothic foot sallied forth from their camp and assailing the Romans from the front; driving them back to the base of the slope. Valens and his men found themselves surrounded, assailed from every direction.
Gratian, the eldest son of Valentian I, was Roman Emperor from 375 to 383. Upon the death of Valentinian in 375, Gratian's half-brother Valentinian II was declared emperor by Valentinian I's soldiers, and the two ruled together. After his uncle Valens, emperor of the East, was killed in the Battle of Adrianople, Gratian essentially became ruler of the entire empire. When this task proved too daunting, he appointed Theodosius I to govern the Eastern empire. He was assassinated in 383.