The Roman emperor was the ruler of the Roman State

Roman Empire

The Roman Empire was the post-Republican period of the ancient Roman civilization, characterised by an autocratic form of government and large territorial holdings in Europe and around the Mediterranean....

 during the imperial period (starting at about 27 BC). The Romans had no single term for the office although at any given time, a given title was associated with the emperor. If a man was "proclaimed emperor" this normally meant he was proclaimed augustus

Augustus

Augustus ;23 September 63 BC – 19 August AD 14) is considered the first emperor of the Roman Empire, which he ruled alone from 27 BC until his death in 14 AD.The dates of his rule are contemporary dates; Augustus lived under two calendars, the Roman Republican until 45 BC, and the Julian...

, or (for generals) imperator

Imperator

The Latin word Imperator was originally a title roughly equivalent to commander under the Roman Republic. Later it became a part of the titulature of the Roman Emperors as part of their cognomen. The English word emperor derives from imperator via Old French Empreur...

(from which English emperor

Emperor

An emperor is a monarch, usually the sovereign ruler of an empire or another type of imperial realm. Empress, the female equivalent, may indicate an emperor's wife or a woman who rules in her own right...

ultimately derives). Several other titles & offices were regularly accumulated by emperors, such as caesar

Caesar (title)

Caesar is a title of imperial character. It derives from the cognomen of Julius Caesar, the Roman dictator...

, princeps senatus

Princeps senatus

The princeps senatus was the first member by precedence of the Roman Senate. Although officially out of the cursus honorum and owning no imperium, this office brought enormous prestige to the senator holding it.-Overview:...

, consul

Consul

Consul was the highest elected office of the Roman Republic and an appointive office under the Empire. The title was also used in other city states and also revived in modern states, notably in the First French Republic...

and pontifex maximus

Pontifex Maximus

The Pontifex Maximus was the high priest of the College of Pontiffs in ancient Rome. This was the most important position in the ancient Roman religion, open only to patricians until 254 BC, when a plebeian first occupied this post...

.