Othman, Or Osman, surnamed "the Conqueror," the founder of the Ottoman empire, and of the present reigning dynasty of Turkey, horn in Bithynia in 1259, died in 1326. He is said to have been the son of Orthogrul, the leader of a horde of Turcomans who had entered the service of the sultan of Roum or of Iconium. Othman succeeded his father in the command, and on the fall of the Seljuk dynasty received part of the province of Bithynia as his share in the division of the sultanate. Immediately afterward he attacked the Byzantine empire, leading his forces in July, 1299, through the unguarded passes of Mt. Olympus, and conquering the territory of Nicaea. The 27 years of Othman's reign were taken up with wars. He reduced the province of Marmora in 1307, and subdued the whole of Bithynia and neighboring provinces. Several times he had been repulsed in attacks upon Nicomedia (Ismid) and Prusa (Brusa); but the capture of the latter place by his son Orkhan, the news of which reached him on his deathbed, laid the foundation of the Turkish empire.

From him it is called the Ottoman Porte; yet it is doubtful whether he ever assumed the title of sultan, although he held a court at Kara-IIissar, and coined money.