Alexios V Doukas (Greek: Ἀλέξιος Δούκας; died December 1204), Latinized as Alexius V Ducas, was Byzantine emperor from February to April 1204, just prior to the sack of Constantinople by the participants of the Fourth Crusade.

[7] By the beginning of 1204, Isaac II and Alexios IV had inspired little confidence among the people of Constantinople with their efforts to protect the city from the Latin crusaders and their Venetian allies, and the citizens were becoming restless.

The crusaders were also losing patience with the emperors; they rioted and set fires in the city when the money and aid promised by Alexios IV was not forthcoming.

He won the approval of the populace by his valour in leading an attack on the Latins at "Trypetos Lithos"; in this clash his mount stumbled and he would have been killed or captured had a band of youthful archers from the city not defended him.

[8][9][10] The citizens of Constantinople rebelled in late January 1204, and in the chaos an otherwise obscure nobleman named Nicholas Kanabos was acclaimed emperor, though he was unwilling to accept the crown.

Instead of contacting the crusaders, Mourtzouphlos, on the night of 28–29 January 1204, used his access to the palace to bribe the "ax-bearers" (the Varangian Guard), and with their backing arrest the emperors.

The young Alexios IV was eventually strangled in prison; while his father Isaac, both enfeebled and blind, died at around the time of the coup, his death variously attributed to fright, sorrow, or mistreatment.

Kanabos was initially spared and offered an office under Alexios V, but he refused both this and a further summons from the emperor and took sanctuary in the Hagia Sophia; he was forcibly removed and killed on the steps of the cathedral.

Choniates states that the meeting was brought to a close by a sudden attack by crusader cavalry on Alexios V and his entourage, the emperor narrowly escaping capture.

The forcible expulsion of all Latins resident in Constantinople in March seems to have been the tipping point which led the crusaders to begin actively negotiating amongst themselves regarding the partition of the Byzantine Empire.

Alexios V then boarded a fishing boat and fled the city towards Thrace on the night of 12 April 1204, accompanied by Eudokia Angelina and her mother Euphrosyne Doukaina Kamatera.

In the Hagia Sophia Constantine Laskaris was acclaimed as emperor, but being unable to persuade the Varangians to continue the fight, in the early hours of 13 April he also fled, leaving Constantinople under crusader control.

In his trial the blind ex-emperor argued that it was Alexios IV who had committed treason to his country, through his intention to invite the crusaders to enter Constantinople in force.

[26] The new, alien, Latin regime of conquerors in Constantinople may have viewed the public trial and execution of the man who murdered the last "legitimate emperor" as a way to cast an aura of legitimacy on themselves.