Peter ( ) (fl. 860s–870s) was a Bulgarian noble and relative of knyaz (khan) Boris I (r. 852–889) who was in charge of diplomatic missions during the Christianization of Bulgaria. His position in the Bulgarian administrative hierarchy is unknown but it has been suggested that he had the title kavhan, i. e. the second person in the state after the monarch.
Historical background
When Boris I assumed the throne of Bulgaria in 852, the country was still pagan, with the ruling Bulgar elite being Tengriists while the Slavic population practised its own religion. Christianity was already widespread in Bulgaria as the country was established on former territories of the Byzantine Empire, and seems to have been influential. Even one of the sons of Khan Omurtag (r. 814–831), Enravota, converted to Christianity. The Bulgarian nobility was strongly opposed to any form of Byzantine influence in the country and was therefore hostile to Christianity as it was directly associated with the Byzantine Empire. Boris I, however, had many reasons to consider conversion — Bulgaria was situated between two powerful Christian empires, Byzantium and East Francia; Christian doctrine particularly favoured the position of the monarch as God's representative on Earth; and finally, Boris also saw Christianity as a way to overcome the differences between Bulgars and Slavs. The geopolitical situation in the mid 9th century was also favourable because of the increasing friction and rivalry between the Papacy in Rome and the Ecumenical Patriarchate of Constantinople for influence in Central Europe. That struggle between the two churches would give the Bulgarian ruler the opportunity to manoeuvre and negotiate with both, thus extracting favourable concessions while keeping the country out of direct foreign influence. When the Byzantines invaded Bulgaria in the autumn of 863 and demanded conversion to Christianity from Constantinople as the single condition to retreat, Boris I readily accepted and was baptised in the beginning of 864, assuming the Christian name Michael after his spiritual godfather, the Byzantine Emperor Michael III. That step was very unpopular among the nobility, but when they rebelled Boris I dealt decisively with them and executed 52 magnates along with their whole families. When in the following year the Byzantines sturdily demonstrated their determination not to allow the existence of an autocephalous Bulgarian Church, Boris I decided to turn to the Papacy.
Missions to Rome
According to the historical sources there were three Bulgarian missions to the Pope with the participation of Peter, the first one being in the summer of 866. The interest of Boris I in the Roman Church was caused by the reluctance of the Ecumenical Patriarchate of Constantinople to accept his request to appoint an independent patriarch (or at least an archbishop) for the Bulgarian diocese in order to retain it subordinated to Constantinople. Boris I was determined to make Bulgaria Christian while keeping the country's religious and political independence. Since the end of the 850s the churches of Rome and Constantinople were in a period of a heated competition for influence over the Slavs and the Ecumenical Church power. This rivalry favoured Boris' plans, as it gave him the opportunity to play one side off against the other and choose. The new orientation of the Bulgarian policy also allowed Boris I to calm down the nobility of the boyars, which was cautious and hostile to the increased Byzantine influence in the country after the Christianization.
First mission
The first Bulgarian delegation arrived before Pope Nicholas I on 29 August 866 — the very same year during which Boris quelled the rebellion of the boyars against Christianization. Among the gifts presented to the Pope by the delegation was the weapon of Boris "with which [he] was armed when in the name of Christ he celebrated over his enemies". The Bulgarians also brought a document with questions by their ruler to the Pope. The content of the questions is reproduced on paragraph 106 of the "Answers of Pope Nicolas to the questions of the Bulgarians". The arrival of the Bulgarian envoys in Rome was a very important event. The Pope enthusiastically spread the news in a letter to Hincmar of Reims and the other archbishops of the Frankish Empire.
That Bulgarian mission was mentioned thirteen years later (June 879) in a letter to Boris I, with which Pope John VIII tried to prevent Bulgaria from returning to the Patriarchate of Constantinople. That letter proves Peter's participation in the mission of 866: