Beyazid I, 1347-1403, Ottoman sultan (1389-1402), son and successor of Murad I. He besieged Byzantine Emperor Manuel II at Constantinople, then overcame the Turkish rulers in E Anatolia and defeated the army of Sigismund of Hungary (see Sigismund, Holy Roman emperor) at Nikopol. Ottoman expansion led to conflict with the conqueror Timur, and the two armies met at Ankara in 1402. Beyazid's troops consisted only of Serbs and the Janissaries, since the Tatars and most of his Turkish vassals had deserted him. His army was routed, and he died as Timur's prisoner. His sons fought (1402-13) each other for the succession; Muhammad I emerged victorious. The name appears in other forms, e.g., Bajazet, Bayazid, and Beyazit.