[2] When Bulgaria converted to Christianity in the ninth century, the ruler Boris I (852–889) was using the title knyaz (prince).

[7] From Bulgaria's complete independence from the Ottomans in 1908 until the abolition of the monarchy in 1946, Bulgarian monarchs once more used the title tsar,[8] though this time generally translated internationally as "king" rather than "emperor".

The only title known from contemporary sources is kanasubigi, recorded in ten Greek-language inscriptions (as ΚΑΝΑΣΥΒΙΓΙ) from the ninth century in reference to Omurtag (814–831) and his son Malamir (831–836).

[10] Upon his conversion to Christianity in 864/865, Boris I (852–889) adopted the new ruling title knyaz, generally translated as "prince" (though sometimes alternatively as "king").

Simeon aspired to make Bulgaria into the new "universal monarchy" (a role the Byzantines viewed themselves as having) by absorbing and replacing the empire centered in Constantinople.

[13] The second empire's third ruler, Kaloyan (1196–1207), adopted the grander title "Emperor of Bulgarians and Vlachs" (imperator Bulgarorum et Blachorum).

[16] His extended title was later revived by Ivan Alexander (1331–1371), who also proclaimed himself as the "Emperor and Autocrat of the Bulgarians and Greeks"[16] to challenge the authority of the then weakened Byzantine Empire.

[18] The use of double names by Bulgarian monarchs, sometimes not used consistently in contemporary sources,[a] has in cases led to confusion and misunderstanding in modern efforts to assign regnal numbers.

[19] References to political developments within Bulgaria prior to the reign of Krum (c. 803–814) are extremely scant, making the dates and family relationships of the rulers recorded in contemporary and later sources highly uncertain.

[18] Following the gradual conquest of Bulgaria in the 14th and 15th centuries, the Ottomans incorporated the Bulgarian lands into the vast province of Rumelia.

[66] In the late 16th century, the new province of Silistra was created due to persistent northern attacks from the Cossacks.