Church Slavonic language in the context of "Rurik"

The First Bulgarian Empire (Church Slavonic: блъгарьско цѣсарьствиѥ, romanized: blŭgarĭsko tsěsarǐstvije; Bulgarian: Първо българско царство) was a medieval state that existed in Southeastern Europe between the 7th and 11th centuries AD. It was founded in 680–681 after part of the Bulgars, led by Asparuh, moved south to the northeastern Balkans. There they secured Byzantine recognition of their right to settle south of the Danube by defeating – possibly with the help of local South Slavic tribes – the Byzantine army led by Constantine IV. During the 9th and 10th century, Bulgaria at the height of its power spread from the Danube Bend to the Black Sea and from the Dnieper River to the Adriatic Sea and became an important power in the region competing with the Byzantine Empire.

As the state solidified its position in the Balkans, it entered into a centuries-long interaction, sometimes friendly and sometimes hostile, with the Byzantine Empire. Bulgaria emerged as Byzantium's chief antagonist to its north, resulting in several wars. The two powers also enjoyed periods of peace and alliance, most notably during the Second Arab Siege of Constantinople, where the Bulgarian army broke the siege and destroyed the Arab army, thus preventing an Arab invasion of Southeastern Europe. Byzantium had a strong cultural influence on Bulgaria, which also led to the eventual adoption of Christianity in 864. After the disintegration of the Avar Khaganate, the country expanded its territory northwest to the Pannonian Plain. Later the Bulgarians confronted the advance of the Pechenegs and Cumans, and achieved a decisive victory over the Magyars, forcing them to establish themselves permanently in Pannonia.

Simeon I the Great (Church Slavonic: цѣсар҄ь Сѷмеѡ́нъ А҃ Вели́къ; Bulgarian: цар Симеон I Велики, romanized: Simeon I Veliki [simɛˈɔn ˈpɤrvi vɛˈliki]; Greek: Συμεών Αʹ ὁ Μέγας, romanized: Sumeṓn prôtos ho Mégas) ruled over Bulgaria from 893 to 927, during the First Bulgarian Empire. Simeon's successful campaigns against the Byzantines, Magyars and Serbs led Bulgaria to its greatest territorial expansion ever, making it the most powerful state in contemporary Eastern and Southeast Europe. His reign was also a period of unmatched cultural prosperity and enlightenment later deemed the Golden Age of Bulgarian culture.

During Simeon's rule, Bulgaria spread over a territory between the Aegean, the Adriatic and the Black seas. The newly independent Bulgarian Orthodox Church became the first new patriarchate besides the Pentarchy, and Bulgarian Glagolitic and Cyrillic translations of Christian texts spread all over the Slavic world of the time. It was at the Preslav Literary School in the 890s that the Cyrillic alphabet was developed. Halfway through his reign, Simeon assumed the title of "emperor" (Tsar), having prior to that been styled "prince" (Knyaz).

Peter I (Church Slavonic: Петръ А҃; Bulgarian: Петър I; died 30 January 970) was the emperor (tsar) of Bulgaria from 27 May 927 to 969. Facing Bogomilism and rebellions by his brothers and also by Časlav Klonimirović early on in his reign, Peter secured more success later in life; he ensured the retreat of the invading Rus by inciting Bulgaria's allies, the Pechenegs, to attack Kiev itself. Traditionally seen as a weak ruler who lost land and prestige, recent scholarship challenges this view, emphasizing the empire's affluence and internal peace. Considered a good ruler during the Middle Ages, his name was adopted by later leaders trying to restore Bulgarian independence under Byzantine rule to emphasize legitimacy and continuity.

Boris II (Church Slavonic: Борисъ В҃; Bulgarian: Борис II; c. 931 – 977) was the emperor (tsar) of Bulgaria from 969 to 977 (in Byzantine captivity from 971).

A knyaz, also knez, knjaz or kniaz (Church Slavonic: кънѧѕь, romanized: kŭnędzĭ), is a historical Slavic title, used both as a royal and noble title in different times. It is usually translated into English as 'prince', 'king' or 'duke', depending on specific historical context and the potentially known Latin equivalents at the time; the word was originally derived from the common Germanic *kuningaz ('king').

Feminine forms of the word may be divided into two groups:

Boris I (also Bogoris), venerated as Saint Boris I (Mihail) the Baptizer (Church Slavonic: Борисъ / Борисъ-Михаилъ, Bulgarian: Борис I / Борис-Михаил; died 2 May 907), was the ruler (knyaz) of the First Bulgarian Empire from 852 to 889. Despite a number of military setbacks, the reign of Boris I was marked with significant events that shaped Bulgarian and European history. With the Christianization of Bulgaria in 864, paganism was abolished. A skillful 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 nobility's concerns about Byzantine interference in Bulgaria's internal affairs.

When in 885 the disciples of Saints Cyril and Methodius were banished from Great Moravia, Boris I gave them refuge and provided assistance which saved the Glagolithic and later promoted the development of the Cyrillic script in Preslav and the Slavic 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 what is now known as Old Church Slavonic.

The Primary Chronicle, shortened from the common Russian Primary Chronicle (Church Slavonic: Повѣсть времѧньныхъ лѣтъ, romanized: Pověstĭ vremęnĭnyxŭ lětŭ, commonly transcribed Povest' vremennykh let (PVL), lit. 'Tale of Bygone Years'), is a chronicle of Kievan Rus' from about 850 to 1110. It is believed to have been originally compiled in the Kiev area in the 1110s. Tradition ascribed its compilation to the monk Nestor (Nestor's Chronicle) beginning in the 12th century, but this is no longer believed to have been the case.

The title of the work, Povest' vremennykh let ("Tale of Bygone Years") comes from the opening sentence of the Laurentian text: "These are the narratives of bygone years regarding the origin of the land of Rus', the first princes of Kiev, and from what source the land of Rus' had its beginning". The work is considered a fundamental source for the earliest history of the East Slavs.

David (Church Slavonic: Даві́дъ Bulgarian: Давид; died 976) was a Bulgarian noble, brother of Emperor Samuel and eldest son of komes Nicholas, member of the Cometopuli dynasty. After the disastrous invasion of Rus' armies and the fall of North-eastern Bulgaria under Byzantine occupation in 971, he and his three younger brothers took the lead of the defence of the country. They executed their power together and each of them governed and defended a separate region. He ruled the southernmost parts of the realm from Prespa and Kastoria and was responsible for the defence the dangerous borders with Thessalonica and Thessaly. In 976 he participated in the major assault against the Byzantine Empire but was killed by vagrant Vlachs between Prespa and Kostur.