Osman I (ōsmän´) or Othman I (ōthmän´), 1259–1326, leader of the Ottoman Turks and founder of the dynasty that established and ruled the Ottoman Empire. The Osmanli or Ottoman Turks derive their name from Osman. He proclaimed (1290) his independence from his overlord, the Seljuk Turks, upon the collapse of their empire. Aided by an influx of Muslim warriors, he expanded his state in NW Asia Minor at the expense of the petty Christian lords who were his neighbors. He nevertheless inaugurated a policy of religious tolerance. Just before his death in 1326, his son and successor, Orkhan, took the city of Bursa from the Byzantines.