Nepos was the husband of the niece of the Eastern Roman emperor Leo, and was named as emperor in the West by Leo in 474, in order to end the reign of the usurper Glycerius, who had been raised to the throne by a German Magister militum (or Master of Soldiers) in the western capital of Ravenna. Officially, however, Leo was sole emperor in such a case and had the right to select a new western Augustus. He chose Nepos, the governor of the province of Dalmatia, and in June 474, Nepos entered Ravenna, was accepted as emperor and forced Glycerius to step down. Glycerius was shunted off to Dalmatia as bishop of the city of Salona, where they later crossed paths again.
As emperor, Nepos tried to consolidate the empire's remaining holdings, which consisted of Italy and footholds in northern and southern Gaul. He was able to renegotiate a recently concluded peace settlement with the Visigoths and their king Euric, which restored the Provence region of Gaul to imperial control in exchange for some other, minor territories which Nepos was unable to maintain firm control over. But he was less successful in negotiating with Geiseric, the King of the Vandals, who was up to his old tricks in launching pirate attacks on Italy. Having recently made peace with the eastern empire, Geiseric saw no need to make concessions to Nepos.
Nepos was, by all accounts, one of the more capable of the late western emperors, but he was unpopular with the Roman Senate, which disliked him for his close ties to the east. When Nepos made a mistake and appointed the untrustworthy Orestes as his master of soldiers, this came back to haunt him.
On August 28, 475, Orestes took control of the government at Ravenna and forced Nepos to flee by ship to Dalmatia. Since he couldn't become emperor himself, as a German, he appointed his son Romulus, who was born to his Roman wife, as the new emperor. Although the boy was probably no more than 10 years old, Orestes gave him the name Romulus Augustus. Known to history as Romulus Augustulus, he is usually considered as the last Roman emperor in the west.
However, Nepos continued to rule in Dalmatia as the rightful western emperor, and continued to be recognized as such by the court in Constantinople. When Odoacer captured Ravenna, killed Orestes and deposed Romulus on September 4, 476, he proclaimed himself King of Italy and asked the eastern emperor Zeno to legalize his position as a patrician officer of the Roman Empire. Zeno did so, but insisted that he recognize Nepos as western emperor. Odoacer did this, and even issued coins in Nepos' name throughout Italy.
The arrangement might have continued for many years had not other things taken place. The first was that Nepos, in about 479, began to plot against Odoacer, hoping to regain control of Italy for himself. Another, perhaps (sources aren't sure on this) is that Glycerius, who was still bishop of Salona, was plotting revenge against Nepos. What is certain is that Odoacer was determined to get rid of him.
He was murdered by his soldiers on one of three dates -- April 25, May 9 or June 22 -- of 480. The April 25 date is probably the correct one. Almost immediately, Odoacer invaded Dalmatia, defeated a force led by the Roman general Ovida on December 9, and added the province to his own kingdom. Adding fuel to the suspicions about Glycerius is a report that Odoacer then made him bishop of the large city of Mediolanum (modern Milan).
Glycerius (473 - 474)
Romulus Augustus (475 - 476)