Alexius V Ducas Murtzouphlos, Byzantine emperor, was proclaimed emperor on February 5, 1204, during the siege of Constantinople by the Latins (Fourth Crusade). His nickname "Murtzouphlos" referred to his extremely bushy eyebrows. He was related to the imperial Angelus family.

His elevation was the result of a revolution in the city against Isaac II and Alexius IV. He conducted the defence with great bravery until it became hopeless (April 12), whereupon he fled. He attempted to ally with his fellow ex-emperor Alexius III against the Latins, but Alexius III had him blinded and delivered into the hands of the crusaders, who put him to death by casting him from the top of the Pillar of Theodosius as the murderer of Alexius IV. He was the last Byzantine emperor before the establishment of the Latin Empire, which controlled Constantinople for the next 57 years.