(Modified from the wikipedia article)

Alexius IV Angelus (b. 16th June, 1182 — d. 8th February, 1204) was a prince and later briefly emperor of the Byzantine Empire, and son of the once deposed and then briefly reinstated emperor Isaac II Angelus (b. 26th September, 1156 — d. 12th February, 1204) and his first wife, Herina Palaiologus (who died less than a year after his birth). Alexius was not a “prince of the purple”, as he was nearly three years of age when his father, with the popular support of the mob of Constantinople, deposed the tyrant Andronicus I (last of the Comnenus dynasty), and took the throne.

While initially successful, with a victory over the Sicilian Normans in the Balkans, Isaac’s rule quickly degenerated into farce. To pay for his armies as well as a dynastic marriage to the daughter of King Bela III of Hungary (Margaret, older sister of King Emeric and Prince Andras), he levied heavy taxes on the provinces. This resulted in the Bulgarian Uprising, and the loss of much of Byzantium’s stability and revenue in the West. A number of his most trusted generals and governors revolted against his authority, and still more used his lax rulership to enrich themselves at the expense of the people. The once mighty Byzantine fleet was allowed to rot and diminish to the point where only thirty decrepit galleys remained, with practically no stocks of the infamous Greek Fire that ensured its supremacy in the Aegean and Black Seas. The trading houses and galleys of Venice gained mercantile and naval power because of his poor government and spendthrift ways, for Isaac was most happy enriching his palaces and churches than anything else.

The rule of Isaac II ended in 1195 when he was overthrown in a coup by his own brother, who was crowned Alexius III. Isaac was blinded and imprisoned, and Alexius III also imprisoned young Alexius, Margaret and her two sons by Isaac, Manuel and John. Alexius III feared to murder the family, remembering well the backlash against Andronicus Comnenus for his parricide of his nephew, Alexius II. Sadly for the people of Byzantium, Alexius III took Isaac’s excesses even farther, spending even more recklessly and placing incompetent sycophants in the most important positions in his government.

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. Alexius’ sister Irene, otherwise lauded as “the rose without a thorn, the dove without guile” by the famous Minnesinger Walther von der Vogelweide, constantly agitated her husband to aid her family in regaining the throne. So it was that over Christmas of 1202, Alexius was introduced to an ally of Phillip’s who might be of service to him, Marquis Boniface I of Montferrat.

Boniface was Philip’s cousin, and he had been chosen to lead the Fourth Crusade the year before, though he had temporarily left the Crusade around the siege of Zara to visit Philip. Alexius and Philip approached the Marquis and discussed with him the possibility of diverting the Crusade to Constantinople so that Isaac could be restored to his throne, with his son ruling as co-emperor; in return, Alexius promised to ameliorate the difficulties besetting the militi Christi.

He 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. Even so, while the young prince was indeed a gifted speaker and possessed of a clever mind, his words alone did not bear fruit. Boniface of Montferrat was no stranger to the east, having fought the Normans with his brother Conrad some twenty years before on Isaac’s behalf. He had heard boasts then of the extraordinary treasury of the emperor, and had seen the wonders of Constantinople with his own eyes. Naturally, the great nobleman agreed to put the proposal to his fellow counts and barons, and Alexius accompanied Boniface back to Zara.

Much of the fleet had moved on to Corfu, but the Venetian Doge Enrico Dandolo was approached and he saw the merit of the proposal. Together they sailed to Corfu, stopping in at Durazzo on the way. The jubilation with which the local populace greeted the prince; their calls for him to take the throne and their professions of loyalty, convinced them further that the diversion to Constantinople was not just necessary, but just. Once they arrived at the island, they expended considerable efforts to convince their fellows but alas, not all of the crusaders have agreed. The Fourth Crusade almost dissolved once the diversion was announced, but after Alexius publicly stated his offer, with the backing of the remaining Abbots as well as Marquis Boniface, Count Baldwin, Count Hugh, Sir Geoffrey and the rest, the dissenters relented.

On their way to the capital, the crusade conquered a number of Aegean islands as well as a number of strategic towns in the Dardanelles. With each victory, Alexius was shown to the towns and cities of the Eastern Empire in order to communicate the rightful cause of the crusade. When they arrived at the Queen of Cities herself, he 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. Alexius III Angelus was also unwilling to concede the throne, and war was soon declared.

On July 17th, 1203, the Crusaders launched an assault on the city, and despite his superior position and numbers, Alexios IIIbizarrely retreated from battle. That night he stole much of the treachery and 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 Alexius IV co-emperor on August 1.

One of his first acts after gaining power was to make the Patriarchate of Constantinople subservient to the Pope of Rome, a move which did little to endear him to his people or his church. He then replaced the absent patriarch, John X Camateros (who had fled with Alexius III) with the Venetian Thomas Morisini, which incensed them still further. Even so, with the crusade as his allies, Alexius IV’s rule was assured.

His power secured, young Alexius IV ordered an audit of the imperial finances. It was soon apparent, even to his fiscally inexperienced mind, that he had made promises that he could not easily keep. The treasury had become sorely depleted since the reign of Manuel Comnenus, and the tax receipts of the empire were not what they once were, owing to the loss of regional stability and loyalty during the reigns of Andronicus I, Isaac II and Alexius III. Even so, by appropriating Church funds and other treasures, as well as confiscating the property of his enemies and leveraging “donations” from would-be allies, Alexius managed to produce a deposit roughly 30 000 silver marks in short order. This was barely 1/7th of what he promised, and after further negotiations he declared an Imperial Processional to enforce his authority and collect outstanding tax receipts from the provinces.

During the Processional, he and his Crusader allies defeated Alexius III on several more occasions. They looted those towns that had harboured the former emperor, easing the debt somewhat further. For the most part, the Processional was merely a show of force, intended to stamp Alexius IV’s authority on those local potentates that had been withholding tax revenues from the capital. It was a qualified success, garnering significant revenues to pay the crusade off. Together with the revenues raised from stripping a great many churches and monasteries of their wealth as well as a variety of donations from noble families to the empire (including those loyal to Petronius and the Cult of the Archangel), the Processional funnelled over 50 000 silver marks to the treasury. Another 100 000 were gleaned from the melting down of precious church artifacts and icons, which he unsuccessfully attempted to keep secret from the citizenry.

Unfortunately, a terrible fire broke out within Constantinople in November, while the Imperial Processional was still abroad. The resulting loss of life and property, compounded by the rioting and looting that took place in its wake, was devastating to the city. Many thousands of Constantinopolitans were left with neither food nor shelter as winter fell, and the citizenry looked to Alexius IV and Isaac II to direct some of their newly gathered wealth towards relief. This they did, although the extraordinary extravagance with which the imperial court conducted its already lavish affairs increased as well.

The signals were missed by neither the people of Byzantium nor the 4th Crusade. Sharp criticisms of the rule of the Angeloi circulated on the streets, while a number of crusader delegations were sent to the Blachernae to press Alexius IV and Isaac II for payment of outstanding monies. In response, the young emperor withdrew from his attempts to win over the hoi polloi, and ceased visiting his erstwhile friends and supporters in the Crusader camp at Galata. More and more, he seemed to be pandering to the opinions of his own courtiers rather than Boniface and those who gave him his throne. Over Christmas and into the new year, Frankish delegates were rebuffed with increasing arrogance and agitation, as Alexius grew accustomed to his power and resentful of the crusade’s part in securing it.

Finally, in the first days of AD 1204, hostilities broke out once again between the city of Constantinople and the 4th Crusade. Negotiations continued, but skirmishing across the Golden Horn became almost a daily occurrence.

One of the Angeloi’s courtiers, Alexius “Mourzouphlos” Ducas, had long desired to return his family to their former imperial glory. Despite his offices and dignity, his intrigues had seen him imprisoned by Alexius III in AD 1200. Now freed from jail and pardoned by Alexius and Isaac after their return to power, Mourzouphlos apparently saw how facile and empty the Angeloi power had become, and despite his public professions of loyalty he was apparently far from grateful for his release. He had spent the months of the crusader occupation of Galata secretly agitating against them both at court and on the street. He ceaselessly promoted himself as the anti-Latin leader that the _Romaioi_were clamouring for, and his nefarious schemes soon paid off. Alexius IV, relatively untried and untested in navigating the treacherous waters of Byzantine politics, was completely fooled by the conspiracies of his advisor.

Over January, Alexius Ducas’ leadership of skirmishes on the Golden Horn dramatically raised his standing among the citizenry. When they rebelled against the rule of the Angeloi in late January, the emperor’s barricaded themselves in the Blachernae Palace and trusted their “loyal ally” to help them get word to Galata. He was to carry the message that they acceded to the 4th Crusade’s demands in return for one last fight in their favour. Obviously they chose the wrong man for the job…

Instead, with widespread public and noble support, Mourzouphlos deposed Alexius IV and Isaac II in a coup on January 27th. Young Alexius was thrown into prison, where he died “of a sudden illness” on the 8th of February, just 3 days after Mourzouphlos had himself crowned Alexius V. Isaac II, in great grief, fear and trepidation for his own life, conveniently succumbed to illness several days later. Alexius V made a great show of publicly mourning his predecessors, and granted them state funerals to keep up appearances.

Despite their recent acrimony, the crusaders were incensed by the murder of their erstwhile emperor and they swiftly called for revenge against the usurper and the people of Byzantium. This was largely sparked by the rumour (perhaps true, but quite likely spread by the agents of Marquis Boniface of Montferrat) that the villain Alexius Mourzouphlos Ducas strangled Alexius IV with his own hands after three attempts to poison the young Angelus failed.