Simeon Saxe-Coburg-Gotha in the context of "1946 Bulgarian republic referendum"

Tsar (/zɑːr, (t)sɑːr/; also spelled czar, tzar, or csar; Bulgarian: цар, romanized: tsar; Russian: царь, romanized: tsar'; Serbian: цар, car) is a title historically used by Slavic monarchs. The term is derived from the Latin word caesar, which was intended to mean emperor in the European medieval sense of the term—a ruler with the same rank as a Roman emperor, holding it by the approval of another emperor or a supreme ecclesiastical official—but was usually considered by Western Europeans to be equivalent to "king".

Tsar and its variants were the official titles in the First Bulgarian Empire (681–1018), Second Bulgarian Empire (1185–1396), the Kingdom of Bulgaria (1908–1946), the Serbian Empire (1346–1371), and the Tsardom of Russia (1547–1721).The first ruler to adopt the title tsar was Simeon I of Bulgaria. Simeon II, the last tsar of Bulgaria, is the last person to have held this title.

Saxe-Coburg and Gotha (German: Sachsen-Coburg und Gotha), or Saxe-Coburg-Gotha (German: Sachsen-Coburg-Gotha [ˈzaksn̩ ˈkoːbʊʁk ˈɡoːta]), was an Ernestine duchy in Thuringia ruled by a branch of the House of Wettin, consisting of territories in the present-day states of Thuringia and Bavaria in Germany. It lasted from 1826 to 1918. In November 1918, Charles Edward, Duke of Saxe-Coburg and Gotha, was forced to abdicate. In 1920, the northern part of the duchy (since 1918 the Free State of Gotha; culturally and linguistically Thuringian) was merged with six other Thuringian free states to form the Free State of Thuringia: Saxe-Weimar-Eisenach (until 1918 a grand duchy), Saxe-Altenburg and Saxe-Meiningen (until 1918 duchies), Schwarzburg-Rudolstadt and Schwarzburg-Sondershausen (until 1918 principalities), as well as the People's State of Reuss (until 1918 the principalities of Reuss-Gera and Reuss-Greiz). The southern part of the duchy (since 1918 the Free State of Coburg; culturally and linguistically Franconian), as southernmost of the Thuringian states, was the only one which, after a referendum, became part of the Free State of Bavaria.

The name Saxe-Coburg-Gotha also refers to the family of the ruling House of Saxe-Coburg and Gotha, which played many varied roles in the dynastic and political history of Europe in the 19th and 20th centuries. In the early part of the 20th century, before the First World War, it was the family of the sovereigns of the United Kingdom, Belgium, Portugal, Bulgaria, and Saxe-Coburg-Gotha. In 1910, the Portuguese king was deposed, and the same thing occurred in Saxe-Coburg-Gotha in 1918 and in Bulgaria in 1946 (although effective control had already ceased two years prior due to a coup). As of 2025, a branch of the family still reigns in Belgium, and while the British line still technically exists up to the present day, it now uses the name Windsor due to a proclamation issued by King George V in 1917. The former Tsar of Bulgaria, Simeon II (reigned 1943–46), kept his surname while serving as the Prime Minister of Bulgaria from 2001 to 2005.

Regnal numbers are ordinal numbers—often written as Roman numerals—used to distinguish among persons with the same regnal name who held the same office, notably kings, queens regnant, popes, and rarely princes and princesses.

It is common to start counting either since the beginning of the monarchy, or since the beginning of a particular line of state succession. For example, Boris III of Bulgaria and his son Simeon II were given their regnal numbers because the medieval rulers of the First and Second Bulgarian Empire were counted as well, although the recent dynasty dates only back to 1878 and is only distantly related to the monarchs of previous Bulgarian states. On the other hand, the kings of England and kings of Great Britain and the United Kingdom are counted starting with the Norman Conquest. That is why the son of Henry III of England is called Edward I, even though there were three English monarchs named Edward before the Conquest (they were distinguished by epithets instead).

The National Movement for Stability and Progress (Bulgarian: Национално движение за стабилност и възход, romanized: Natsionalno dvizhenie za stabilnost i vazhod, NDSV) is a liberal, populist political party in Bulgaria. It was known as the National Movement Simeon II (Bulgarian: Национално движение „Симеон Втори“, romanized: Natsionalno dvizhenie "Simeon Vtori") until 3 June 2007.

The party was created as a personal vehicle of Simeon of Saxe-Coburg-Gotha (Simeon II), the last Bulgarian Tsar (albeit nominally), who was deposed following the 1944 Bulgarian coup d'état, for his successful bid to become Prime Minister of Bulgaria in 2001. Simeon served as prime minister until 2005 and the party remained part of the governing coalition until 2009, when they lost all their seats in the National Assembly.

Parliamentary elections were held in Bulgaria on 17 June 2001. The result was a victory for the new National Movement – Simeon II, which won 120 of the 240 seats. Following the elections, Simeon Saxe-Coburg-Gotha, the country's last Tsar, who was deposed by the Bulgarian Communist Party in 1946, became prime minister.

Nikola Mihaylov Mihov (Bulgarian: Никола Михайлов Михов, 11 December 1891 – 1 February 1945) was a Bulgarian lieutenant general of artillery who served as one of the three Regents of Bulgaria for the underage Simeon II (1943–44).