Alexios V Doukas, 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. His family name was Doukas, but he was also known by the nickname Mourtzouphlos or Murtzuphlus (Μούρτζουφλος), referring to either bushy, overhanging eyebrows or a sullen, gloomy character. He achieved power through a palace coup, killing his predecessors in the process. Though he made vigorous attempts to defend Constantinople from the crusader army, his military efforts proved ineffective. His actions won the support of the mass of the populace, but he alienated the elite of the city. Following the fall, sack, and occupation of the city, Alexios V was blinded by his father-in-law, the ex-emperor Alexios III, and later executed by the new Latin regime. He was the last Byzantine emperor to rule in Constantinople until the Byzantine recapture of Constantinople in 1261.

Isaac II Angelos or Angelus was Byzantine Emperor from 1185 to 1195, and co-Emperor with his son Alexios IV Angelos from 1203 to 1204. In a 1185 revolt against the Emperor Andronikos Komnenos, Isaac seized power and rose to the Byzantine throne, establishing the Angelos family as the new imperial dynasty.