Career
Before being proclaimed emperor in 1185, Petar IV was named Theodore (Todor). The change of name indicates an attempt to seek legitimacy through a connection with the sainted Emperor Petar I of Bulgaria, whose name was also adopted by earlier rebels against Byzantine rule in 1040 and 1072. The name appears augmented as Slavopetăr ("glorious Petar") and Kalopetăr ("good Petar") in some sources.
The rebellion failed to immediately capture Bulgaria"s historic capital Preslav, but established a new capital city at Tărnovo, presumably the center of the revolt.
In 1186 the rebels suffered a defeat, but Isaac II Angelos failed to exploit his victory and returned to Constantinople. With the help of the chiefly Cuman population north of the Danube, Peter IV and Ivan Asen recovered their positions and raided into Thrace.
When Isaac II Angelos penetrated into Moesia again in 1187 he failed to capture either Tărnovo or Loveč, and he signed a treaty effectively recognizing the Second Bulgarian Empire. During the Third Crusade, as relations between Isaac II Angelos and Frederick I, Holy Roman Emperor deteriorated, Peter IV and Ivan Asen offered military assistance to the German crusaders at Niš in 1189.
In 1190 Isaac II Angelos managed to advance on Tărnovo again and besieged it, but was forced to retreat because of the progress of Cuman reinforcements from the north.
During his retreat, the Byzantine emperor was ambushed by Ivan Asen, who had taken over the Balkan passes, and Isaac II barely escaped with his life, losing much of his army and treasures. The victory over the Byzantines brought Ivan Asen to the fore, and Petar IV had apparently already crowned him co-emperor in 1189. With Ivan Asen I left in charge of Tărnovo and the campaigns against the Byzantines, Petar IV retired to Preslav without abdicating the throne.
After the murder of Ivan Asen I in 1196, Petar IV marched on Tărnovo, besieged the murderer Ivanko, and forced him to flee to the Byzantines.
About a year later, in 1197, Peter IV was also murdered.
