Roman emperor
The Roman emperor was the ruler and monarchial head of state of the Roman Empire during the imperial period, starting with the granting of the title augustus to Octavian in 27 BC. The emperors used a variety of different titles throughout history. 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 often used was caesar, used for heirs-apparent, and imperator, originally a military honorific. Early emperors also used the title princeps civitatis ("first citizen"). Emperors frequently amassed Republican titles, notably princeps senatus, consul, and pontifex maximus. The legitimacy of an emperor's rule depended on his control of the Roman army and recognition by the Roman senate; an emperor would normally be proclaimed by his troops, or invested with imperial titles by the Senate, or both. The first emperors reigned alone; later emperors would sometimes rule with co-emperors and divide administration of the empire between them. The Romans considered the office of emperor to be distinct from that of a king. Augustus, the first emperor, resolutely refused recognition as a monarch. For the first three hundred years of Roman emperors, from Augustus until Diocletian, efforts were made to portray the emperors as leaders of the Republic, fearing any association with the kings of Rome prior to the Roman Republic. From Diocletian, whose tetrarchic reforms also divided the position into one emperor in the West and one in the East, emperors ruled until the end of the Empire in an openly monarchic style, and did not preserve the nominal principle of a republic; the contrast with kings was maintained. Although the imperial succession was generally hereditary, it was only hereditary if there was a suitable candidate acceptable to the army and the bureaucracy, so the principle of automatic inheritance was not adopted. Elements of the republican institutional framework (senate, consuls, and magistrates) were preserved even after the end of the Western Empire.