Attempted usurpation by John Komnenos the Fat for the throne of Alexios III Angelos.

John Komnenos, nicknamed "the Fat", was a Byzantine noble who attempted to usurp the imperial throne from Alexios III Angelos in a short-lived coup in Constantinople on 31 July 1201. The coup drew on opposition to the ruling Angelid dynasty among rival aristocratic families and the common people, who were dissatisfied by the dynasty's failures against external foes. John had previously been an obscure figure, but he became the figurehead of the uprising because of his imperial blood, as he was descended from the illustrious Komnenian dynasty (1081–1185). However, the real driving force behind his coup was probably the ambitious Alexios Doukas Mourtzouphlos. With the support of the capital's populace, the plotters managed to seize most of the Great Palace in Constantinople's southeastern corner, which the mob proceeded to loot, and John Komnenos was crowned in the Hagia Sophia. Alexios III, however, was secure in his residence in the northwestern Palace of Blachernae, and he sent forces by sea to land in the part of the Great Palace still held by the loyal Varangian Guard. Most of the urban mob dispersed for the night, and the Varangians had little difficulty in suppressing the coup. John Komnenos was captured and executed with many of his followers.

Alexios III Angelos, Latinized as Alexius III Angelus, was Byzantine Emperor from March 1195 to 17/18 July 1203. He reigned under the name Alexios Komnenos associating himself with the Komnenos dynasty.