Alexios IV Angelos Alexios IV Angelos ( or Alexius IV Angelus ) ( ) ( c . 1182 – February 8 , 1204 ) was Byzantine Emperor from August 1203 to January 1204 . He was the son of Emperor Isaac II Angelus and his first wife Irene . His paternal uncle was Emperor Alexius III Angelus . Prince in exile . The young Alexios was imprisoned in 1195 when Alexios III overthrew Isaac II in a coup . In 1201 , two Pisan merchants were employed to smuggle Alexius out of Constantinople to the Holy Roman Empire , where he took refuge with his brother - in - law Philip of Swabia , King of Germany . While there he met with Marquis Boniface of Montferrat , Philip ' s cousin , who had been chosen to lead the Fourth Crusade , but had temporarily left the Crusade during the siege of Zara to visit Philip . Boniface and Alexios discussed diverting the Crusade to Constantinople so that Alexios could be restored to his father ' s throne ; in return , Alexios would give them 10 , 000 Byzantine soldiers to help fight in the Crusade , maintain 500 knights in the Holy Land , the service of the Byzantine navy ( 20 ships ) in transporting the Crusader army to Egypt , as well as money to pay off the Crusaders ' debt to the Republic of Venice with 200 , 000 silver marks . Additionally , he promised to bring the Greek Orthodox Church under the authority of the pope . Alexios accompanied Boniface back to the Crusader fleet , which had moved on to Corcyra , and the Venetians were in favour of the plan when they learned of it . In 1202 the fleet arrived at Constantinople . Alexios was paraded outside the walls , but the citizens were apathetic , as Alexios III , though a usurper and illegitimate in the eyes of the westerners , was an acceptable emperor for the Byzantine citizens . Emperor . On July 18 , 1203 the Crusaders launched an assault on the city , and Alexios III immediately fled into Thrace . The next morning the Crusaders were surprised to find that the citizens had released Isaac II from prison and proclaimed him emperor , despite the fact that he had been blinded to make him ineligible to rule . The Crusaders could not accept this , and forced Isaac II to proclaim his son Alexios IV co - emperor on August 1 . Despite Alexios ' grand promises , Isaac , the more experienced and practical of the two , knew that the Crusaders ' debt could never be repaid from the imperial treasury . Alexios , however , had apparently not grasped how far the empire ' s financial resources had fallen during the previous fifty years . Alexios did manage to raise half the sum promised ( 100 , 000 silver marks ) , by appropriating treasures from the church and by confiscating the property of his enemies . He then attempted to defeat his uncle Alexios III , who remained in control of Thrace . The sack of some Thracian towns helped Alexios ' situation a little , but meanwhile hostility between the restive Crusaders and the inhabitants of Constantinople was growing . In December 1203 violence exploded between the citizens of Constantinople and the Crusaders . Enraged mobs seized and brutally murdered any foreigner they could lay hands upon , and the Crusaders felt that Alexios had not fulfilled his promises to them . Alexios refused their demands , and is quoted as saying , " " I will not do any more than I have done . " " While relations with the Crusaders were deteriorating , Alexios had become deeply unpopular with the Greek citizenry , and with his own father . Blinded and nearly powerless , Isaac II resented having to share the throne with his son ; he spread rumours of Alexios ' supposed sexual perversity , alleging he kept company with " " depraved men " " . The chronicler Nicetas Choniates dismissed Alexios as " " childish " " and criticized his familiarity with the Crusaders and his lavish lifestyle . At the beginning of January 1204 , Alexios IV retaliated against the Crusaders by setting fire to 17 ships and sending it against the Venetian fleet , but the attempt fails . Deposition and death . At the end of January 1204 , the populace of Constantinople rebelled and tried to proclaim a rival emperor in Hagia Sophia . Alexios IV attempted to reach a reconciliation with the Crusaders , entrusting the anti - western courtier Alexios Doukas " Murzuphlus " with a mission to gain Crusader support . However , Alexios Doukas imprisoned both Alexios IV and his father on the night of January 27 – 28 , 1204 . Isaac II died soon afterwards , possibly of old age or from poison , and Alexios IV was strangled on February 8 . Alexios Doukas was proclaimed emperor as Alexios V . During Alexios IV ' s brief reign , the empire lost its territories along the Black Sea coast to the Empire of Trebizond .