Osman I, or Osman Gazi, was the Oghuz Turkish tribal leader who founded the Ottoman Dynasty and ruled as the first sultan of the Ottoman Empire. Both the dynasty and the Ottoman Empire were named after him. According to the Ottoman tradition, his family hailed from the Kayı branch of the Oghuz Turkish tribe. Osman I founded the empire during the end of the 13th century in the Söğüt town (present-day Bilecik Province) in northwestern Anatolia. Keeping Söğüt as the base, Osman led the Muslim frontier warriors (“Ghazis”) to launch attacks on the Byzantine Empire, which was later conquered by his descendants. The state, which was just a small principality during Osman’s reign, eventually developed into a world empire with the state and the caliphate controlling most of North Africa, Western Asia, and Southeast Europe during the 14th century and the early 20th century. The Ottoman Dynasty ruled the Ottoman Empire till 1922, when the ‘Grand National Assembly of Turkey’ (GNAT) abolished the Ottoman Sultanate, deposing the imperial family from power during the Turkish War of Independence. The Republic of Turkey was declared eventually.