Alexius IV (Alexius Angelus), d. 1204, Byzantine emperor (1203–4), son of Isaac II. When his father was deposed, Alexius fled to Italy and then went to Germany. Encouraged by his brother-in-law, Philip of Swabia, he obtained (1202) from the leaders of the Fourth Crusade (see Crusades) the promise of help in deposing his uncle, Alexius III. Made joint emperor with Isaac II after the Crusaders entered Constantinople, he was overthrown for his subservience to his allies and was strangled by order of Alexius V.
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