Byzantine emperor (1185-1195 and 1203-1204).
The founder of the Angelos dynasty, Isaac came to the throne upon the violent overthrow of the last Komnenian emperor, Andronikos I (12 September 1185). He succeeded in expelling the Norman conquerors of Thessalonica (mod. Thessaloniki, Greece) from Macedonia in 1185-1186, but was unable to subdue either Isaac Komnenos, the rebellious ruler of Cyprus, or the Bulgarian Asenid dynasty, which (with Vlach and Cuman support) established the Second Bulgarian Empire, which Isaac was forced to recognize (1186/1187).
In 1189-1190 the depredations on Byzantine territory by the land army of the Third Crusade (1189-1192) led by the Holy Roman Emperor, Frederick I Barbarossa, resulted in Isaac’s approach to Saladin, Ayyûbid sultan of Egypt; Frederick threatened Constantinople (mod. Istanbul, Turkey) itself and forced Isaac to conclude the Treaty of Adrianople (February 1190), which obliged him to transport the crusader army across the Hellespont to Anatolia. In the early 1190s Isaac faced insurrections by the Serbs and Byzantine pretenders in Anatolia and the Balkans.
In April 1195, while preparing a campaign against the Serbs, Isaac was arrested and blinded by his brother, Alex- ios III Angelos, who seized the throne. Isaac remained a prisoner until August 1203, when he was freed by the victorious army of the Fourth Crusade (1202-1204) and restored to the throne with his son, Alexios IV Angelos, as co-emperor. The two Angeloi were overthrown by a coup led by Alexios V Doukas Mourtzouphlos (January 1204). Isaac died a broken man (28/29 February 1204) a few weeks following the assassination of his son (8 February).