Orkhan (ôr-khän´), 1288?–1362?, Ottoman sultan (1326–1362?), son and successor of Osman I as leader of the Ottoman Turks. He defeated Byzantine Emperor Andronicus III and conquered large parts of Asia Minor, including Nicaea and Izmit. In 1345 the Ottomans first crossed into Europe to aid Byzantine Emperor John VI (John Cantacuzene). Orkhan married John's daughter Theodora. Orkhan crossed the Dardanelles two more times, assisting John against Stephen Dušan of Serbia and gaining for the Ottomans a foothold in Europe. He left a well-organized state to his son and successor, Murad I. Orkhan was the first Ottoman ruler to assume the title of sultan.