Valentinian Dynasty

The Valentinian Dynasty congregates the rule of four emperors, who ruled the Western Roman Empire from 364 to 392 and theEastern Empire from 364 to 378. They were Valentinian I and his sons Gratianus and Valentinianus II (West) and Valens (Valentinianus' brother) and Valentinianius daughter's husband Theodosius I (East).
This dynasty was related to the House of Theodosius by the marriage of Theodosius I to Valentinianus' daughter, and Theodosius grandson Valentinianus III would became western emperor (a.d. 425-455) and the last ruler from both dynasties.
Valentinianus I (a.d. 321-375)

Also known as Valentinian the Great, Flavius Valentinianus Augustus was emperor from 364 to 375. Upon becoming emperor he made his brother Valens his co-emperor, giving him rule of the eastern provinces while Valentinian retained the west.

During his reign, he fought successfully against the Alamanni and Sarmatians. He was also the last emperor to conduct campaigns across both the Rhine and Danube rivers, rebuilding and improving the fortifications along the frontiers. Due to the successful nature of his reign and almost immediate decline of the empire after his death, he is often considered the "last great western emperor".

Gratianus (a.d. 359 - 383)

Flavius Gratianus Augustus was emperor from a.d. 375 to 383. Eldest son of Valentinianus, during his youth Gratian accompanied his father on several campaigns along the Rhine and Danube frontiers. Upon the death of Valentinian in 375, Gratian's brother Valentinianus II was declared emperor by his father's soldiers. In 378, Gratian's generals won a decisive victory over the Alamanni at the Battle of Argentovaria. Gratian subsequently led a campaign across the Rhine, the last emperor to do so. That same year, his uncle Valens was killed in battle against the Goths making Gratian essentially ruler of the entire Roman Empire. He favoured Christianity, refusing the divine attributes of the emperors and removing the Altar of Victory from the Senate in Rome.

Valens (a.d. 328 - 378)
Flavius Julius Valens Augustus was emperor from the Eastern Empire from a.d.364 to 378. He was given the eastern half of the empire by his brother Valentinianus after the latter's accession to the throne. Sometimes called the "last true roman emperor", he was defeated and killed in the Battle of Adrianopolis, event that marked the beginning of the collapse of the decaying Western Empire.