Peter IV (in Bulgarian Petăr IV, or commonly but less accurately Petăr II; Bulgarian: Петър IV) ruled as emperor (tsar) of Bulgaria 1185 - 1197. Together with his brother Asen he managed to restore the Bulgarian Empire after nearly 170 years of Byzantine domination.
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. He was succeeded by his younger brother Ivan (nicknamed Kaloyan or Ivanica/Ioanica), whom he had apparently associated on the throne in 1196.