Julius Nepos, or simply Nepos, ruled as Roman emperor of the West from 24 June 474 to 28 August 475. After losing power in Italy, Nepos retreated to his home province of Dalmatia, from which he continued to claim the western imperial title, with recognition from the Eastern Roman Empire, until he was murdered in 480. Though Nepos' successor in Italy, Romulus Augustulus, is traditionally deemed the last western Roman emperor, Nepos is regarded by some historians as the true last emperor of the west, being the last widely recognised claimant to the position.

The Roman emperor was the ruler and monarchical head of state of the Roman Empire, starting with the granting of the title augustus to Octavian in 27 BC. The term "emperor" is a modern convention, and did not exist as such during the Empire. Often when a given Roman is described as becoming emperor in English, it reflects his taking of the title augustus and later basileus. Another title used was imperator, originally a military honorific, and caesar, originally a surname. Early emperors also used the title princeps alongside other Republican titles, notably consul and pontifex maximus.