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 " Empereur " . The Roman emperors themselves generally based their authority on multiple titles and positions , rather than preferring any single title . Nevertheless , " imperator " was used relatively consistently as an element of a Roman ruler ' s title throughout the principate ( derived from " princeps , " from which " prince " in English is derived ) and the dominate . In Latin , the feminine form of imperator is imperatrix , denoting a ruling " female " . " Imperatores " in the ancient Roman Kingdom . When Rome was ruled by kings , to be able to rule , the king had to be invested with the full regal authority and power . So , after the comitia curiata , held to elect the king , the king also had to be conferred the imperium . " Imperatores " in the Roman Republic . In Roman Republican literature and epigraphy , an imperator was a magistrate with imperium ( Rivero , 2006 ) . But also , mainly in the later Roman Republic and during the late Republican civil wars , " imperator " was the honorifical title assumed by certain military commanders . After an especially great victory , an army ' s troops in the field would proclaim their commander " imperator " , an acclamation necessary for a general to apply to the Senate for a triumph . After being acclaimed " imperator " , the victorious general had a right to use the title after his name until the time of his triumph , where he would relinquish the title as well as his imperium . Since a triumph was the goal of many politically ambitious Roman commanders , Roman Republican history is full of cases where legions were bribed to call their commander " imperator " . The title of " imperator " was given in 90 BC to Lucius Julius Caesar , in 84 BC to Gnaeus Pompeius Magnus , in 60 BC to Gaius Julius Caesar , relative of the previously mentioned Lucius Julius Caesar , in 45 BC again to Gaius Julius Caesar , in 44 BC to Marcus Iunius Brutus , and in 41 BC to Lucius Antonius ( younger brother and ally of the more famous Marcus Antonius ) . In 15 AD Germanicus was also " imperator " during the empire ( see below ) of his adoptive father Tiberius . " Imperator " as an imperial title . After Augustus established the Roman Empire , the title " imperator " was generally restricted to the emperor , though in the early years of the empire it would occasionally be granted to a member of his family . As a permanent title , " imperator " was used as a praenomen by the Roman emperors and was taken on accession . After the reign of Tiberius , the act of being proclaimed imperator was transformed into the act of imperial accession . In fact , if a general was acclaimed by his troops as " imperator " , it would be tantamount to a declaration of rebellion against the ruling emperor . At first the term continued to be used in the Republican sense as a victory title but attached to the " de facto " monarch and head of state , rather than the actual military commander . The title followed the emperor ' s name along with the number of times he was acclaimed as such , for example " IMP V " ( " imperator five times " ) . In time it became the title of the " de facto " monarch , pronounced upon ( and synonymous with ) their assumption . As a title " imperator " was generally translated into Greek as " autokrator " ( " one who rules himself , " also sometimes used as a translation for " Roman dictators " . ) This was necessarily imprecise as it lost the nuances of Latin political thought contrasting " imperium " with other forms of public authority . Nevertheless , this title ( along with " sebastos " for " augustus " ) was used in Greek - language texts for Roman emperors from the establishment of the empire . In 629 CE Emperor Heraclius , having changed the official language to Greek nine years earlier , adopted the title of " basileus " , previously used by Alexander the Great as a translations for emperor and it is thereafter used interchangeably ( and often in conjunction ) with autokrator in the Byzantine Empire . Post - Roman use . After the Roman empire collapsed in the West in the 5th century , Latin continued to be used as the language of learning and diplomacy for some centuries . The Roman emperors of this period ( referred to by modern historians as the Byzantine emperors ) were referred to as " imperatores " in Latin texts , while the word " basileus " ( king ) was used in Greek . After 800 , the " imperator " was used ( in conjunction with " augustus " ) as a formal Latin title in succession by the Carolingian and German Holy Roman Emperors until 1806 and by the Austrian Emperors until 1918 . In 1721 , as part of his drive to both westernize the Russian Empire and assert the monarchy ' s claim that it was the successor to the Byzantine emperors , Peter the Great imported the Latin word directly into Russian and styled himself " imperator " ( Императоръ ) . The style remained the official one for all his successors down to the end of the Russian Empire in 1917 , though the Russian rulers continued to be colloquially known as tsar ( a word derived from " Caesar " ) , which they had begun to use c . 1480 to likewise assert their contention to be the heirs to the Byzantine state ( see : Third Rome . ) Reigning female Russian rulers were styled " imperatritsa . " Napoleon famously adopted the title for himself and after the Napoleonic wars , the number of emperors in Europe proliferated , but Latin began to fall out of use for all but the most ceremonial situations . Still , in those rare cases in which a European monarch ' s Latin titles were used , " imperator " was used as a translation for " emperor " . Famously , after assuming the title Emperor of India , British monarchs would follow their signatures with the initials " RI " , standing for " rex imperator " ( " king - emperor " ) . George VI of the United Kingdom was the last European ruler to claim an imperial title ; when he abdicated as Emperor of India in 1948 , the last active use of the title " imperator " in the West ceased . It was thereafter used only historically , or as a Latin translation for certain continuing titles of non - European cultures , such as Japan . The imperial title was also adopted by Jean - Bédel Bokassa , during his reign as the emperor of the short - lived Central African Empire ( 1976 – 79 ) . Imperatrix . The term imperatrix seems not to have been used in Ancient Rome to indicate the " consort " of an imperator or later of an Emperor . In the early years of the Roman Empire there was no standard title or honorific for the Emperor ' s wife , even the " Augusta " honorific was rather exceptionally granted , and not exclusively to wives of living emperors . It is not clear when the feminine form of the Latin term " imperator " originated or was used for the first time . It usually indicates a " reigning " monarch , and is thus used in the Latin version of titles of modern reigning Empresses . Likewise , when Fortuna is qualified " imperatrix mundi " in the " Carmina Burana " there ' s no implication of any type of " consort " — the term describes ( the Goddess or personified ) Fortune " ruling the world " . In Christian context , " Imperatrix " became a laudatory address to the Virgin Mary , in diverse forms at least since the Middle Ages — for example , she is sometimes called " Imperatrix angelorum " ( " regnant of the angels " ) . Derivatives . " Imperator " is the root of most Romance languages ' word for emperor . It is the root of the English word " emperor " , which entered the language via the French " empereur " , while related adjectives like " imperial " were imported into English directly from Latin . It is also believed to be the ultimate origin of the Serbian term for king .