history of Osman Gazi

  Osman I , also called   Osman Gazi , (born   c.   1258—died 1324 or 1326), ruler of a Turkmen principality in northwestern   Anatolia   who is regarded as the founder of the   Ottoman   Turkish state. Both the name of the   dynasty   and the empire that the dynasty established are derived from the Arabic form (ʿUthmān) of his name. Osman was descended from the Kayı branch of the  Oğuz Turkmen. His father,  Ertugrul, had established a principality centred at  Sögüt. With Sögüt as their base, Osman and the Muslim frontier warriors ( Ghazis) under his command waged a slow and stubborn conflict against the Byzantines, who sought to defend their territories in the hinterland of the Asiatic shore opposite Constantinople (now Istanbul). Osman gradually extended his control over several former Byzantine fortresses, including  Yenişehir, which provided the Ottomans with a strong base to lay siege to  Bursa and  Nicaea (now İznik), in northwestern Anatolia. Osman was succeded by his son Orhan,