Which Byzantine emperor's request for help spurred the First Crusade?

Alexios I Komnenos was the Byzantine emperor whose appeal for Western military aid helped spark the First Crusade. His request arose from the Byzantine Empire’s struggle against the expanding Seljuk Turks in Asia Minor.

Alexios became emperor in 1081, when Byzantine power was under pressure from several enemies. The Seljuks had seized much of Anatolia, including territory vital to the empire’s manpower and tax base. In 1095, Alexios sent envoys to Pope Urban II at the Council of Piacenza, asking for military assistance—likely trained soldiers and mercenaries rather than the enormous popular armies that eventually arrived.

Urban II later preached the First Crusade at the Council of Clermont. The resulting expedition captured Nicaea and helped restore significant parts of western Anatolia to Byzantine control, although relations between Byzantium and the Crusaders soon became tense. Alexios was not himself a Crusader commander; he was the emperor whose diplomatic appeal helped set the movement in motion. Basil II, John II, and Manuel I Komnenos belonged to other periods of Byzantine history.