Alexius III (Alexius Angelus) (əlĕk´sēəs, ăn´jələs), d. after 1210, Byzantine emperor (1195–1203). He acceded to power by deposing and blinding his brother Isaac II. This act served as pretext for the leaders of the Fourth Crusade (see Crusades) to attack Constantinople (1203). The Crusaders made Isaac II and his son Alexius IV coemperors, Alexius III having fled. In 1204, Alexius III's son-in-law was briefly emperor as Alexius V. Another son-in-law, Theodore I, became emperor of Nicaea. Alexius died in obscurity.