Nero, later to become Roman emperor, is given the title princeps iuventutis (head of the youth).

AD 51 (LI) was a common year starting on Friday of the Julian calendar. At the time, it was known as the Year of the Consulship of Caesar and Scipio. The denomination AD 51 for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.

Nero Claudius Caesar Augustus Germanicus was a Roman emperor and the final emperor of the Julio-Claudian dynasty, reigning from AD 54 until his death in AD 68.

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. When a given Roman is described as becoming emperor in English, it generally reflects his accession as augustus, and later as basileus. Another title used was imperator, originally a military honorific, and caesar, originally a cognomen. Early emperors also used the title princeps alongside other Republican titles, notably consul and pontifex maximus.

Princeps is a Latin word meaning "first in time or order; the first, foremost, chief, the most eminent, distinguished, or noble; the first person". As a title, Princeps originated in the Roman Republic wherein the leading member of the Senate was designated princeps senatus. It is primarily associated with the Roman emperors as an unofficial title first adopted by Augustus in 27 BC. Its use in this context continued until the regime of Diocletian at the end of the third century. He preferred the title of dominus, meaning "lord" or "master". As a result, the Roman Empire from Augustus to Diocletian is termed the "principate" (principatus). Other historians define the reign of Augustus to Severus Alexander as the Principate, and the period afterwards as the "Autocracy".