Alexios V Doukas, surnamed Mourtzouphlos (died December 1205) is Byzantine Emperor (5 February – 12 April 1204) during the second and final siege of Constantinople by the participants of the Fourth Crusade.

He is related to the imperial Doukas family.

His nickname "Mourtzouphlos" refers to either his bushy, overhanging eyebrows or his sullen character.

The term has the meaning of one being crestfallen, depressed, despondent, downcast, gloomy, sullen and evidently frowning, scowling.