He is widely regarded as one of the worst Byzantine emperors for calling upon the Fourth Crusade to help him gain power, which ultimately led to the sack of Constantinople.

In 1201, two Pisan merchants were employed to smuggle Alexios out of Constantinople to the Holy Roman Empire, where he took refuge with his brother-in-law Philip of Swabia,[2] King of Germany.

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.

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.

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.

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".

At the beginning of January 1204, Alexios IV retaliated against the Crusaders by setting fire to 17 ships filled with inflammable materials and sending them against the Venetian fleet, but the attempt failed.

[3] At the end of January 1204, the populace of Constantinople rebelled and tried to proclaim a rival emperor Nicholas Canabus who took sanctuary in the Hagia Sophia.

Eventually however, after the deposition of Alexios IV, who was in favor of the crusade, the Byzantines continued to lack the ability to pay off its debt.