Imperator in the context of "Emperor"

The history of the Roman Empire covers the history of ancient Rome from the traditional end of the Roman Republic in 27 BC until the abdication of Romulus Augustulus in AD 476 in the West, and the Fall of Constantinople in the East in 1453. Ancient Rome became a territorial empire while still a republic but was then ruled by emperors, beginning with Octavian Augustus, the final victor of the republican civil wars.

Rome had begun expanding shortly after the founding of the Republic in the 6th century BC, though it did not expand outside the Italian Peninsula until the 3rd century BC, during the Punic Wars, after which the Republic expanded across the Mediterranean. Civil war engulfed Rome in the mid-1st century BC, first between Julius Caesar and Pompey, and finally between Octavian (Caesar's grand-nephew) and Mark Antony. Antony was defeated at the Battle of Actium in 31 BC, leading to the annexation of Egypt. In 27 BC, the Senate gave Octavian the titles of Augustus ("venerated") and Princeps ("foremost"), thus beginning the Principate, the first epoch of Roman imperial history. Augustus' name was inherited by his successors, as well as his title of Imperator ("commander"), from which the term "emperor" is derived. Early emperors avoided any association with the ancient kings of Rome, instead presenting themselves as leaders of the Republic.

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

The legitimacy of an emperor's rule depended on his control of the Roman army and recognition by the Senate; an emperor would normally be proclaimed by his troops, or by the Senate, or both. The first emperors reigned alone; later emperors would sometimes rule with co-emperors to secure the succession or to divide the administration of the empire between them. The office of emperor was thought to be distinct from that of a rex ("king"). Augustus, the first emperor, resolutely refused recognition as a monarch. For the first three hundred years of Roman emperors, efforts were made to portray the emperors as leaders of the Republic, fearing any association with the kings who ruled Rome prior to the Republic.

Autokrator or Autocrator (Ancient Greek: αὐτοκράτωρ, romanized: autokrátōr, lit. 'self-ruler', from αὐτός, autós, 'self' + κράτος, krátos, 'dominion') is a Greek epithet applied to an individual who is unrestrained by superiors. It has been applied to military commanders-in-chief as well as Roman and Byzantine emperors as the translation of the Latin title imperator. Its connection with Byzantine and Russian-style absolutism gave rise to the modern terms autocracy and autocrat.

The Holy Roman Emperor, originally and officially the Emperor of the Romans (Latin: Imperator Romanorum; German: Kaiser der Römer) during the Middle Ages, and also known as the Roman-German Emperor since the early modern period (Latin: Imperator Germanorum; German: Römisch-Deutscher Kaiser), was the ruler and head of state of the Holy Roman Empire. The title was held in conjunction with the title of King of Italy (Rex Italiae) from the 8th to the 16th century, and, almost without interruption, with the title of King of Germany (Rex Teutonicorum, lit. 'King of the Teutons') throughout the 12th to 18th centuries.

The Holy Roman Emperor title provided the highest prestige among medieval Catholic monarchs, because the empire was considered by the Catholic Church to be the only successor of the Roman Empire during the Middle Ages and the early modern period. Thus, in theory and diplomacy, the emperors were considered primus inter pares—first among equals—among other Catholic monarchs across Europe.

A collegium (pl.: collegia) or college was any association in ancient Rome that acted as a legal entity. Such associations could be civil or religious.The word collegium literally means "society", from collega ("colleague"). They functioned as social clubs or religious collectives whose members worked towards their shared interests. These shared interests encompassed a wide range of the various aspects of urban life; including political interests, cult practices, professions, trade, and civic services. The social connections fostered by collegia contributed to their influence on politics and the economy; acting as lobbying groups and representative groups for traders and merchants.

Some collegia were linked to participating in political violence and social unrest, which resulted in the suppression of social associations by the Roman government. Following the passage of the lex Julia during the reign of Julius Caesar as consul and dictator of the Roman Republic (49–44 BC), and their reaffirmation during the reign of Caesar Augustus as princeps senatus and imperator of the Roman Army (27 BC – 14 AD), collegia required the approval of the Roman Senate or the Emperor in order to be authorized as legal bodies.