Romulus Augustus (c. 460–465  – c. 511–530), nicknamed Augustulus, was Roman emperor of the West from 31 October 475 until 4 September 476. Romulus was placed on the imperial throne while still a minor by his father Orestes, the magister militum, for whom he served as little more than a figurehead. After a rule of ten months, the barbarian general Odoacer defeated and killed Orestes and deposed Romulus. As Odoacer did not proclaim any successor, Romulus is typically regarded as the last Western Roman emperor, his deposition marking the end of the Western Roman Empire as a political entity. The deposition of Romulus Augustulus is also sometimes used by historians to mark the transition from antiquity to the medieval period.

Very few records survive of Romulus's reign. There are no known policies, laws or inscriptions of significance of the emperor, which leaves the impression that he was a shadowy and relatively inconsequential figure. The nickname "Augustulus" means "little Augustus" and was a derisive reference to his young age. Romulus's immediate family, including his father and possibly his mother, and maybe both his paternal and maternal grandparents, were from the Roman province of Pannonia, and many of his family members had military backgrounds.

Romulus came to power through the usurpation of his predecessor Julius Nepos (r. 474–475 in Italy) in 475. Nepos fled to Dalmatia and continued to claim the imperial title in exile, which hampered Romulus's legitimacy and ensured that he was never recognised by the Eastern Roman emperor Zeno. In 476, the allied barbarian foederati in Italy demanded Italian lands to settle on, which was refused by Orestes. Under Odoacer, the foederati defeated and killed Orestes and deposed Romulus, whereafter Odoacer became the first King of Italy and accepted Emperor Zeno as his nominal superior.

Romulus's life was spared by Odoacer, and he was allowed to retire to the castellum Lucullanum, a great fortress in Campania. Little certain information is known concerning Romulus's life in exile. He might have played a role in founding a monastery at castellum Lucullanum in the 480s or 490s, dedicated to Saint Severinus of Noricum. Romulus could have been alive as late as 507 or 511 when Theodoric the Great, Odoacer's successor, wrote a letter to a "Romulus" concerning a pension, but was likely dead before his mid-40s, as accounts of the eastern Roman invasion of Italy at that time do not mention him.

Romulus Augustus' birth name was simply Romulus; he was named after his maternal grandfather, a nobleman from Poetovio in Noricum. Upon his accession to the imperial throne, he also took Augustus as a proper name, not just a title. Many historians have noted the coincidence that the last western emperor bore the names of both Romulus, the legendary founder and first king of Rome, and Augustus, the first emperor. The full style used on his coinage was Dominus Noster Romulus Augustus Pius Felix Augustus. Romulus Augustus was often colloquially referred to as "Augustulus" (meaning "little Augustus") even in his own time, in reference to his youth. "Augustulus" was a derisive nickname and was never in official use; all of Romulus' coins use the names Romulus Augustus. In Greek, his first name Romulus was also changed derisively into the nickname Momylus ("little disgrace").

By the time of emperor Diocletian (r. 284–305), the idea that the Roman Empire had grown so large that it would be better managed by two co-ruling emperors, rather than one, had become established. After various divisions were made throughout the 4th century, the empire was firmly and permanently divided into a western and eastern sphere of imperial administration from the death of emperor Theodosius I (r. 379–395) in 395 onwards. Though modern historians typically use the terms Western Roman Empire and Eastern Roman Empire to describe the new political situation, the Romans themselves never considered the empire to have been formally divided, still viewing it as a single unit, although most often having two rulers rather than one. Over the course of the 5th century, the western empire experienced a period of catastrophic decline. Not only were many of the rulers in the west generally lacking in competence, but they also faced enormous problems. In comparison with the eastern provinces, much of the west was more rural, with fewer people and a less stable economy. An increasing number of Germanic barbarian invasions and settlements throughout the west only added to these issues.

In 410, the Visigoths under Alaric I had sacked Rome and in 455, the last western emperor of Theodosius' dynasty, Valentinian III (r. 425–455), was deposed and murdered. That same year, Rome was sacked again for the second time in less than fifty years, this time by the Vandals. The Roman army became increasingly reliant on barbarian mercenaries and after Valentinian's murder, the most powerful barbarian generals, such as Ricimer (c. 418–472), became politically dominant, ruling through proclaiming puppet emperors. In the twenty years between the death of Valentinian and the accession of Romulus Augustus, eight different emperors ruled in the west. By 475, the western empire was in critical condition. Outside of Italy, authority was only exercised in Raetia and some regions of Gaul.

The ruling emperor in 475 was Julius Nepos, who had been in power for less than a year. Nepos had been appointed western emperor in 474 by the eastern emperors Leo I (r. 457–474) and Zeno (r. 474–491), but had little real support in the west. In 475, Nepos named Orestes as a patrician and magister militum ('master of soldiers'; effectively commander-in-chief), replacing the previous holder of that office, Ecdicius. Orestes was a distinguished late Roman figure, once having served as notarius (secretary) to the Hunnic king Attila. As magister militum, Orestes was tasked by Nepos to lead an army against Visigoths and Burgundians, foederati (barbarian allies of the empire) who were rebelling in southern Gaul. The army given to Orestes by Nepos was multi-ethnic, with many foederati soldiers. Heeding the grievances of his troops (among other things learning that Nepos had refused requests for land grants ), Orestes defied the emperor's orders and marched on Ravenna, the capital of the western empire. On 28 August 475, Orestes entered Ravenna with his army and Nepos escaped across the Adriatic Sea to Salona in Dalmatia.