Emperor from 1185 after a reign of war and tumult, he was dethroned, blinded and imprisoned by his brother Alexius in 1195. Because of this, his son Alexius fled to the court of Philip of 
Schwaben, an uncle by marriage, and involved the Germans in the political manoeuvres which surrounded the launching of the Fourth Crusade in 1202. 
Isaac II was restored in 1203, reigned six months, was again dethroned, and died in prison. Constantinople fell to Latin forces on 12 April 1204 amidst scenes of carnage and pillage which shocked even hardened contemporaries.
 

Source:  Leo van de Pas