Boris I, also known as Boris-Mihail (Michael) and Bogoris (Bulgarian: Борис I / Борис-Михаил; died 2 May 907) was the Knyaz (Prince) of First Bulgarian Empire in 852–889. At the time of his baptism in 864, Boris was named Michael after his godfather, Emperor Michael III. The historian Steven Runciman called him one of the greatest persons in history.

Despite a number of military setbacks, the reign of Boris I was marked with significant events that shaped the Bulgarian and Slavic history. With the Christianization of Bulgaria the country abolished the traditional state religion Tengriism. A skilful diplomat, Boris I successfully exploited the conflict between the Patriarchate of Constantinople and the Papacy to secure an autocephalous Bulgarian Church, thus dealing with the concerns among the nobility for strong Byzantine interference in the internal matters of the country.

When in 885 the disciples of Saints Cyril and Methodius were banished from Great Moravia, Boris I gave them refuge and provided assistance to develop the Slavic alphabet and literature. After he abdicated in 889, his eldest son and successor tried to restore the old pagan religion but was deposed by Boris I. During the Council of Preslav which followed that event, the Byzantine clergy was replaced with Bulgarian and the Greek language was replaced with Old Church Slavonic as an official language of the Church and the state.

Coordinates: 42°45′N 25°30′E / 42.75°N 25.5°E / 42.75; 25.5

Bulgaria ⁱ/bʌlˈɡɛəriə/ (Bulgarian: България, IPA: [bɤ̞ɫˈɡarijɐ]), is a country located in Southeastern Europe. It is bordered by Romania to the north, Serbia and the Macedonia to the west, Greece and Turkey to the south and the Black Sea to the east. With a territory of 110,994 square kilometres (42,855 sq mi), Bulgaria is Europe's 14th-largest country. Its location has made it a historical crossroad for various civilisations and as such it is the home of some of the earliest metalworking, religious and other cultural artifacts in the world.

Prehistoric cultures began developing on Bulgarian lands during the Neolithic period. Its ancient history was marked by the presence of the Thracians, and later by the Greeks and Romans. The emergence of a unified Bulgarian ethnicity and state dates back to the First Bulgarian Empire, which dominated most of the Balkans and functioned as a cultural hub for Slavic peoples during the Middle Ages. With the downfall of the Second Bulgarian Empire in 1396, its territories came under Ottoman rule for nearly five hundred years. The Russo-Turkish War of 1877–1878 resulted in the Third Bulgarian State, recognised in 1908. The following years saw several conflicts with its neighbours, which prompted Bulgaria to align with Germany in both World Wars. In 1946 it became a Communist republic with a single-party system until 1989, when the Communist Party allowed multi-party elections. After 1990 Bulgaria transitioned to democracy and a market-based economy.

Boris III the Unifier, Tsar of Bulgaria (30 January 1894 – 28 August 1943), originally Boris Klemens Robert Maria Pius Ludwig Stanislaus Xaver (Boris Clement Robert Mary Pius Louis Stanislaus Xavier), son of Ferdinand I, came to the throne in 1918 upon the abdication of his father, following the defeat of the Kingdom of Bulgaria during World War I. This was the country's second major defeat in only five years, after the disastrous Second Balkan War (1913). Under the Treaty of Neuilly, Bulgaria was forced to cede new territories and pay crippling reparations to its neighbours, thereby threatening political and economic stability. Two political forces, the Agrarian Union and the Communist Party, were calling for the overthrowing of the monarchy and the change of the government. It was in these circumstances that Boris succeeded to the throne.

Boris was born on 30 January 1894 in Sofia. He was the first son of Prince Ferdinand of Bulgaria and his wife Princess Marie Louise.

In February 1896 his father paved the way for the reconciliation of Bulgaria and Russia with the conversion of the infant Prince Boris from Roman Catholicism to Eastern Orthodox Christianity, a move that earned Ferdinand the frustration of his wife, the animosity of his Catholic Austrian relatives (particularly that of his uncle, Francis Joseph of Austria) and excommunication from the Catholic Church. In order to remedy this difficult situation Ferdinand christened all his remaining children as Catholics. Nicholas II of Russia stood as godfather to Boris and met the young boy during Ferdinand's official visit to Saint Petersburg in July 1898.