Emperor

Therefore, a king might be obliged to pay tribute to another ruler,[3] or be restrained in his actions in some unequal fashion, but an emperor should in theory be completely free of such restraints.

Ancient Romans abhorred the name Rex ("king"), and it was critical to the political order to maintain the forms and pretenses of republican rule.

Diocletian sought to address the challenges of the Empire's now vast geography and the instability caused by the informality of succession by the creation of co-emperors and junior emperors.

Although the empire was again subdivided and a co-emperor sent to Italy at the end of the fourth century, the office became unitary again only 95 years later at the request of the Roman Senate and following the death of Julius Nepos, last Western Emperor.

This change was a recognition of the reality that little remained of Imperial authority in the areas that had been the Western Empire, with even Rome and Italy itself now ruled by the essentially autonomous Odoacer.

Although this principle was held by all emperors after Constantine, it met with increasing resistance and ultimately rejection by bishops in the west after the effective end of Imperial power there.

The Principality of Achaea, a vassal state the empire had created in Morea (Greece) intermittently continued to recognize the authority of the crusader emperors for another half century.

Byzantium's close cultural and political interaction with its Balkan neighbors Bulgaria and Serbia, and with Russia (Kievan Rus', then Muscovy) led to the adoption of Byzantine imperial traditions in all of these countries.

He wished to maintain his and his family's Imperial status in the event that the Holy Roman Empire should be dissolved, as it indeed was in 1806 when an Austrian-led army suffered a humiliating defeat at the Battle of Austerlitz.

The new imperial title may have sounded less prestigious than the old one, but Francis' dynasty continued to rule from Austria and a Habsburg monarch was still an emperor (Kaiser), and not just merely a king (König), in name.

[12][13] In 913, Simeon I of Bulgaria was crowned Emperor (Tsar, originally more fully Tsesar, cěsar') of his own people by the Patriarch of Constantinople and Imperial regent Nicholas Mystikos outside the Byzantine capital.

[18] Nevertheless, the Bulgarian imperial title was recognized by its neighbors and trading partners, including Byzantium, Hungary, Serbia, Venice, Genoa, Dubrovnik.

[19] After Bulgaria obtained full independence from the Ottoman Empire in 1908, its monarch, who was previously styled Knyaz, Prince, took the traditional title of Tsar, this time translated as King.

[20] The kings of the Ancien Régime and the July Monarchy used the title Empereur de France in diplomatic correspondence and treaties with the Ottoman emperor from at least 1673 onwards.

During his reign, he also set about creating the Second Mexican Empire (headed by his choice of Maximilian I of Mexico, a member of the House of Habsburg), to regain France's hold in the Americas and to achieve greatness for the 'Latin' race.

The title was not exactly hereditary but self-proclaimed by those who had, wholly or partially, united the Christian northern part of the Iberian Peninsula, often at the expense of killing rival siblings.

After the end of Roman rule in Britain, the Imperator Cunedda forged the Kingdom of Gwynedd in northern Wales, but all his successors were titled kings and princes.

During the rule of Henry VIII the Statute in Restraint of Appeals declared that 'this realm of England is an Empire...governed by one Supreme Head and King having the dignity and royal estate of the imperial Crown of the same'.

Hence England and, by extension its modern successor state, the United Kingdom of Great Britain and Northern Ireland, is according to English law an Empire ruled by a King endowed with the imperial dignity.

[27] The government led by Prime Minister Benjamin Disraeli, conferred the additional title upon her by an Act of Parliament, reputedly to assuage the monarch's irritation at being, as a mere Queen, notionally inferior to the emperors of Russia, Germany, and Austria.

[28] The Indian Imperial designation was also formally justified as the expression of Britain succeeding the former Mughal Emperor as suzerain over hundreds of princely states.

The Indian Independence Act 1947 provided for the abolition of the use of the title "Emperor of India" by the British monarch, but this was not executed by King George VI until a royal proclamation on 22 June 1948.

Under the guise of idealism giving way to realism, German nationalism rapidly shifted from its liberal and democratic character in 1848 to Prussian prime minister Otto von Bismarck's authoritarian Realpolitik.

Atahualpa may actually be considered a usurper as he had achieved power by killing his half-brother and he did not perform the required coronation with the imperial crown mascaipacha by the Huillaq Uma (high priest).

After the declaration of independence on 15 September 1821, it was the intention of the Mexican parliament to establish a commonwealth whereby the king of Spain, Ferdinand VII, would also be Emperor of Mexico, but in which both countries were to be governed by separate laws and with their own legislative offices.

The full style of the Ottoman sultan once the empire's frontiers had stabilized became:[39][40] Sultan (given name) Khan, Sovereign of The Sublime House of Osman, Sultan us-Selatin (Sultan of Sultans), Hakan (Khan of Khans), Commander of the faithful and Successor of the Prophet of the Lord of the Universe, Custodian of the Holy Cities of Mecca, Medina and Quds (Jerusalem), Padishah (Emperor) of The Three Cities of Istanbul (Constantinople), Edirne (Adrianople) and Bursa, and of the Cities of Châm (Damascus) and Cairo (Egypt), of all Azerbaijan, of the Maghreb, of Barkah, of Kairouan, of Alep, of the Arab and Persian Iraq, of Basra, of El Hasa strip, of Raqqa, of Mosul, of Parthia, of Diyâr-ı Bekr, of Cilicia, of the provinces of Erzurum, of Sivas, of Adana, of Karaman, of Van, of Barbaria, of Habech (Abyssinia), of Tunisia, of Tripoli, of Châm (Syria), of Cyprus, of Rhodes, of Crete, of the province of Morea (Peloponnese), of Bahr-i Sefid (Mediterranean Sea), of Bahr-i Siyah (Black Sea), of Anatolia, of Rumelia (the European part of the Empire), of Bagdad, of Kurdistan, of Greece, of Turkestan, of Tartary, of Circassia, of the two regions of Kabarda, of Gorjestan (Georgia), of the steppe of Kipchaks, of the whole country of the Tatars, of Kefa (Theodosia) and of all the neighbouring regions, of Bosnia, of the City and Fort of Belgrade, of the province of Sirbistan (Serbia), with all the castles and cities, of all Arnaut, of all Eflak (Wallachia) and Bogdania (Moldavia), as well as all the dependencies and borders, and many others countries and cities.After the Ottoman capture of Constantinople in 1453, the Ottoman sultans began to style themselves Kaysar-i Rum (Ceaser of the Romans) as they asserted themselves to be the heirs to the Roman Empire by right of conquest.

After the defeat of the Italians by the British and the Ethiopians in 1941, Haile Selassie was restored to the throne but Victor Emmanuel did not relinquish his claim until 1943, even though he had no standing to the title.

The title was briefly revived from 12 December 1915 to 22 March 1916 by President Yuan Shikai and again in early July 1917 when General Zhang Xun attempted to restore last Qing emperor Puyi to the throne.

However, shortly after the announcement that Princess Kiko was pregnant with her third child, the proposal to alter the Imperial Household Law was suspended by then-Prime Minister Junichiro Koizumi.

In the end, Đinh Bộ Lĩnh unified the country after defeating all the warlords and became the first ruler of Đại Việt to use the title Hoàng Đế (皇帝, Emperor) in 968.