Who was the Byzantine prince who promised rewards to the Fourth Crusade in 1203?

The Byzantine prince who promised rewards to the Fourth Crusade in 1203 was Alexios IV Angelos. He sought Western military help to restore his imprisoned and deposed father, Isaac II Angelos, to the Byzantine throne.

Alexios met leaders connected with the crusade while in exile in the West. His proposal offered the expedition substantial financial and military support if the Crusaders diverted from their route to Egypt and helped him regain Constantinople. His promises included 200,000 silver marks, 10,000 Byzantine troops, naval assistance, and support for bringing the Greek Orthodox Church under papal authority.

The Crusaders accepted the plan and reached Constantinople in June 1203. Alexios was installed as co-emperor with Isaac II on 1 August, but the imperial treasury could not meet the promised payments. He managed to raise roughly half the money, while opposition to the Crusaders and to religious concessions grew inside the city.

Alexios IV was overthrown in January 1204 and killed soon afterward. His failure to satisfy the agreement helped turn the expedition against Constantinople itself. The city was captured and sacked in April 1204, a dramatic reversal of the crusade’s original goal of recovering Jerusalem.