EMPEROR (Fr. empereur, from the Lat. imperator), a title formerly borne by the sovereigns of the Roman empire (see Empire), and since their time, partly by derivation, partly by imitation, used by a variety of other sovereigns. Under the Republic, the term imperator applied in theory to any magistrate vested with imperium; but in practice it was only used of a magistrate who was acting abroad (militiae) and was thus in command of troops. The term imperator was the natural and regular designation employed by his troops in addressing such a magistrate; but it was more particularly and specially employed by them to salute him after a victory; and when he had been thus saluted he could use the title of imperator in public till the day of his triumph at Rome, after which it would lapse along with his imperium. The senate itself might, in the later Republic, invite a victorious general to assume the title; and in these two customs - the salutation of the troops, and the invitation of the senate - we see in the germ the two methods by which under the Empire the princeps was designated; while in the military connotation attaching to the name even under the Republic we can detect in advance the military character by which the emperor and the Empire were afterwards distinguished. Julius Caesar was the first who used the title continuously (from 58 B.C. to his death in 44 B.C.), as well domi as militiae; and his nephew Augustus took a further step when he made the term imperator a praenomen, a practice which after the time of Nero becomes regular. But apart from this amalgamation of the term with his regular name, and the private right to its use which that bestowed, every emperor had an additional and double right to the title on public grounds, possessed as he was of an imperium infinitum majus, and commanding as he did all the troops of the Empire. From the latter point of view - as generalissimo of the forces of Rome, he had the right to the insignia of the commander (the laurel wreath and the fasces), and to the protection of a bodyguard, the praetoriani. This public title of imperator was normally conferred by the senate; and an emperor normally dates his reign from the day of his salutation by the senate. But the troops were also regarded as still retaining the right of saluting an imperator; and there were emperors who regarded themselves as created by such salutation and dated their reigns accordingly. The military associations of the term thus resulted, only too often, in making the emperor the nominee of a turbulent soldiery.
Augustus had been designated (not indeed officially, but none the less regularly) as princeps - the first citizen or foremost man of the state. The designation suited the early years of the Empire, in which a dyarchy of princeps and senate had been maintained. But by the 2nd century the dyarchy is passing into a monarchy: the title of princeps recedes, and the title of imperator comes into prominence to designate not merely the possessor of a certain imperium, or the general of troops, but the simple monarch in the fulness of his power as head of the state. From the days of Diocletian one finds occasionally two emperors, but not, at any rate in theory, two Empires; the two emperors are the dual sovereigns of a single realm. But from the time of Arcadius and Honorius (A.D. 395) there are in reality (though not in theory) two Empires as well as two emperors, one of the East and one of the West. When Greek became the sole language of the East Roman Empire, imperator was rendered sometimes by and sometimes by , the former word being the usual designation of a sovereign, the latter specially denoting that despotic power which the imperator held, and being in fact the official translation of imperator. Justinian uses as his formal title, and as the popular term.
On the revival of the Roman empire in the West by Charlemagne in 800, the title (at first in the form imperator, or imperator Augustus, afterwards Romanorum imperator Augustus) was taken by him and by his Frankish, Italian and German successors, heads of the Holy Roman Empire, down to the abdication of the emperor Francis II. in 1806. The doctrine had, however, grown up in the earlier middle ages (about the time of the emperor Henry II., 1002-1024) that although the emperor was chosen in Germany (at first by the nation, afterwards by a small body of electors), and entitled from the moment of his election to be crowned in Rome by the pope, he could not use the title of emperor until that coronation had actually taken place. The German sovereign, therefore, though he exercised, as soon as chosen, full imperial powers both in Germany and Italy, called himself merely "king of the Romans" (Romanorum rex semper Augustus) until he had received the sacred crown in the sacred city. In 1508 Maximilian I., being refused a passage to Rome by the Venetians, obtained from Pope Julius II. a bull permitting him to style himself emperor elect (imperator electus, erwählter Kaiser). This title was taken by Ferdinand I. (1558) and all succeeding emperors, immediately upon their coronation in Germany; and it was until 1806 their strict legal designation, and was always employed by them in proclamations and other official documents. The term "elect" was, however, omitted even in formal documents when the sovereign was addressed or was spoken of in the third person.
In medieval times the emperor, conceived as vicegerent of God and co-regent with the pope in government of the Christian people committed to his charge, might almost be regarded as an ecclesiastical officer. Not only was his function regarded as consisting in the defence and extension of true religion; he was himself arrayed in ecclesiastical vestments at his coronation; he was ordained a subdeacon; and assisting the pope in the celebration of the Eucharist, he communicated in both kinds as a clerk. The same sort of ecclesiastical character came also to be attached to the tsars  of Russia, who - especially in their relations with the Orthodox Eastern Church - may vindicate for themselves (though the sultans of Turkey have disputed the claim) the succession to the East Roman emperors (see Empire). But the title of emperor was also used in the middle ages, and is still used, in a loose and vague sense, without any ecclesiastical connotation or hint of connexion with Rome (the two attributes which should properly distinguish an emperor), and merely in order to designate a non-European ruler with a large extent of territory. It was thus applied, and is still applied, to the rulers of China and Japan; it was attributed to the Mogul sovereigns of India; and since 1876 it has been used by British monarchs in their capacity of sovereigns of India (Kaiser-i-Hind). 
Since the French Revolution and during the course of the 19th century the term emperor has had an eventful history. In 1804 Napoleon took the title of "Emperor of the French," and posed as the reviver of the Empire of Charlemagne. Afraid that Napoleon would next proceed to deprive him of his title of Holy Roman Emperor, Francis II. first took the step, in 1804, of investing himself with a new title, that of "Hereditary Emperor of Austria," and then, in 1806, proceeded to the further step of abdicating his old historical title and dissolving the Holy Roman Empire. Thus the old and true sense of the term emperor - the sense in which it was connected with the church in the present and with Rome in the past - finally perished; and the term became partly an apanage of Bonapartism (Louis Napoleon resuscitated it as Napoleon III. in 1853), and partly a personal title of the Habsburgs as rulers of their various family territories. In 1870, however, a new and most important use of the title was begun, when the union of Germany was achieved, and the Prussian king, who became the head of united Germany, received in that capacity the title of German Emperor. Here the title of emperor designates the president of a federal state; and here the Holy Roman emperor of the 17th and 18th centuries, the president of a loose confederation of German states, may be said to have found his successor. But the term has been widely and loosely used in the course of the 19th century. It was the style from 1821 to 1889 of the princes of the house of Braganza who ruled in Brazil; it has been assumed by usurpers in Haiti, and in Mexico it was borne by Augustin Iturbide in 1822 and 1823, and by the ill-fated Archduke Maximilian of Austria from 1864 to 1867. It can hardly, therefore, be said to have any definite descriptive force at the present time, such as it had in the middle ages. So far as it has any such force in Europe, it may be said partly to be connected with Bonapartism, and to denote a popular but military dictatorship, partly to be connected with the federal idea, and to denote a precedence over other kings possessed by a ruler standing at the head of a composite state which may embrace kings among its members. It is in this latter sense that it is used of Germany, and of Britain in respect of India; it is in something approaching this latter sense that it may be said to be used of Austria.
See J. Selden, Titles of Honour (1672); J. Bryce, Holy Roman Empire (London, 1904); and Sir E. Colebrooke, "On Imperial and Other Titles" in the Journal of the Royal Asiatic Society (1877). See also the articles on "Imperator" and "Princeps" in Smith's Dictionary of Greek and Roman Antiquities (1890).
 The word Tsar, like the German Kaiser, is derived from Caesar (see Tsar). Peter the Great introduced the use of the style "Imperator," and the official designation is now "Emperor of all the Russias, Tsar of Poland, and Grand Duke of Finland," though the term tsar is still popularly used in Russia.
 For the titles of , imperator Augustus, etc., applied in the 10th century to the Anglo-Saxon kings, see Empire (note). The claim to the style of emperor, as a badge of equal rank, played a considerable part in the diplomatic relations between the Sultan and certain European sovereigns. Thus, at a time when this style (Padishah) was refused by the Sultan to the tsars of Russia, and even to the Holy Roman Emperor himself, it was allowed to the French kings, who in diplomatic correspondence and treaties with Turkey called themselves "emperor of France" (empereur de France). - [Ed.].
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)