Alexios IV Angelos in the context of "Angelos"

The Latin Empire, also referred to as the Latin Empire of Constantinople or the Constantinopolitan Empire, was a feudal Crusader state founded by the leaders of the Fourth Crusade on lands captured from the Byzantine Empire. The Latin Empire was intended to replace the Byzantine Empire as the Western-recognized Roman Empire in the east, with a Catholic emperor enthroned in place of the Eastern Orthodox Roman emperors. The main objective to form a Latin Empire was planned over the course of the Fourth Crusade, promoted by crusade leaders such as Boniface I of Montferrat, as well as the Republic of Venice.

The Fourth Crusade had originally been called to retake the Muslim-controlled city of Jerusalem, but a sequence of economic and political events culminated in the Crusader army sacking the city of Constantinople, the capital of the Byzantine Empire. Originally, the plan had been to restore the deposed Byzantine Emperor Isaac II Angelos, who had been usurped by Alexios III Angelos, to the throne. The crusaders had been promised financial and military aid by Isaac's son Alexios IV, with which they had planned to continue to Jerusalem. When the crusaders reached Constantinople, the situation quickly turned volatile, and while Isaac and Alexios briefly ruled, the crusaders did not receive the payment they had hoped for. In April 1204, they captured and plundered the city's enormous wealth.

Isaac II Angelos or Angelus (Greek: Ἰσαάκιος Κομνηνός Ἄγγελος, romanized: Isaákios Komnēnós Ángelos; September 1156 – 28 January 1204) was Byzantine Emperor from 1185 to 1195, and co-Emperor with his son Alexios IV Angelos from 1203 to 1204. In an 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.

His father Andronikos Doukas Angelos was a military leader in Asia Minor (c. 1122 – aft. 1185) who married Euphrosyne Kastamonitissa (c. 1125 – aft. 1195). Andronikos Doukas Angelos was the son of Constantine Angelos and Theodora Komnene (b. 15 January 1096/1097), the youngest daughter of Emperor Alexios I Komnenos and Irene Doukaina. Thus Isaac was a member of the extended imperial clan of the Komnenoi.

The siege of Constantinople in 1203 was a crucial episode of the Fourth Crusade, marking the beginning of a series of events that would ultimately lead to the fall of the Byzantine capital. The crusaders, diverted from their original mission to reclaim Jerusalem, found themselves in Constantinople, in support of the deposed emperor Isaac II Angelos and his son Alexios IV Angelos. The besieging forces, primarily composed of Western European knights faced initial setbacks, but their determination and advanced siege weaponry played a pivotal role in pressuring the Byzantine defenders.

Amidst the chaos, the Byzantine emperor was overthrown, leading to a power vacuum and setting the stage for the more infamous events of 1204 when the crusaders, frustrated by unpaid debts and political turmoil, eventually sacked the city. This marked the first time in nearly nine centuries that Constantinople fell to an external force, forever altering the course of Byzantine history.

Alexios III Angelos (Medieval Greek: Ἀλέξιος Ἄγγελος, romanized: Aléxios Ángelos; c. 1153 – 1211), Latinized as Alexius III Angelus, was Byzantine Emperor from March 1195 to 17/18 July 1203. He reigned under the name Alexios Komnenos (Ἀλέξιος Κομνηνός; Aléxios Komnēnós) associating himself with the Komnenos dynasty (from which he was descended cognatically).

A member of the extended imperial family, Alexios came to the throne after deposing, blinding and imprisoning his younger brother Isaac II Angelos. The most significant event of his reign was the attack of the Fourth Crusade on Constantinople in 1203, on behalf of Alexios IV Angelos.