The monarchs of Bulgaria ruled the country during three periods of Bulgaria's history as an independent country: from the establishment of the First Bulgarian Empire in 681 to the Byzantine conquest of Bulgaria in 1018; from the Uprising of Asen and Peter that established the Second Bulgarian Empire in 1185 to the annexation of the rump Bulgarian state into the Ottoman Empire in 1396; and from the re-establishment of an independent Bulgaria in 1878 to the abolition of monarchy in a referendum held on 15 September 1946.
Early Bulgarian rulers possibly used the title Kanasubigi (possibly related to Khan, Khagan) before the 7th century and until the 9th century. The title knyaz (prince) was used for a brief period by Boris I of Bulgaria (and his two successors) after the Christianization of Bulgaria in 864.
The title tsar (emperor), the Bulgarian form of the Latin Caesar, was first adopted and used in Bulgaria by Simeon I the Great (son of Knyaz Boris I), following a decisive victory over the Byzantine Empire in 913. It was also used by all of Simeon I's successors until the fall of Bulgaria under Ottoman rule in 1396. After Bulgaria's liberation from the Ottomans in 1878, its first monarch Alexander I adopted the title knyaz, or prince. However, when de jure independence was proclaimed under his successor Ferdinand in 1908, the title was elevated to the customary tsar once more, but this time in the sense of king. The use of tsar continued under Ferdinand and later under his heirs Boris III and Simeon II until the abolition of monarchy in 1946. While the title tsar is translated as "emperor" in the cases of the First and Second Bulgarian Empires, it is translated as "king" in case of the Third Bulgarian State in the 20th century.
In the few surviving medieval Bulgarian royal charters, the monarchs of Bulgaria styled themselves as "In Christ the Lord Faithful Emperor and Autocrat of all Bulgarians" or similar variations, sometimes including “... and Romans, Greeks, or Vlachs".
In 705 the Eastern Roman Emperor Justinian II gave the title caesar to the Bulgarian ruler Tervel, the first foreigner to receive this title.The Pope Innocent III did not accept Kaloyan's claim to an imperial crown, but dispatched Cardinal Leo Brancaleoni to Bulgaria in early 1204 to crown him with the title of King of the Bulgarians and Vlachs.This list does not include the mythical Bulgar rulers and the rulers of Old Great Bulgaria listed in the Nominalia of the Bulgarian khans as well as unsuccessful claimants to the throne who are not generally listed among the Bulgarian monarchs, neither rulers of Volga Bulgaria, or other famous Bulgarian rulers as Kuber or Alcek.
The early Bulgarian ruler Kubrat, as important allied foreign ruler, was granted the title of Patrikios (Patrician) by the Eastern Roman Emperor. His ring A was inscribed in Greek XOBPATOY and ring C was inscribed XOBPATOY ПATPIKIOY, indicating the dignity of Patrikios (Patrician) that he had achieved in the Byzantine world.

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