Osman I (bornc. 1258—died 1324 or 1326) was the ruler of a Turkmen principality in northwesternAnatolia who is regarded as the founder of theOttoman Turkish state. Both the name of thedynasty 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 theOğuz Turkmen. His father,Ertugrul, had established a principality centred atSögüt. With Sögüt as their base, Osman and the Muslim frontier warriors (Ghazis) under his command waged a slow and stubborn conflict against theByzantines, who sought to defend their territories in the hinterland of the Asiatic shore opposite Constantinople (now Istanbul). Osman gradually extended his control over several formerByzantine fortresses, includingYenişehir, which provided the Ottomans with a strong base to lay siege toBursa andNicaea (now İznik), in northwestern Anatolia. Osman was succeded by his sonOrhan, who captured Bursa on April 6, 1326. Ottoman tradition holds that Osman died just after the capture of Bursa, but some scholars have argued that his death should be placed in 1324, the year of Orhan’s accession.