Born in 1258, Osman I (Osman Khan or Osman Bey) established a dynasty that would become the Ottoman Empire. Leader of the Turkish Kayi Tribe, Osman was given the task of defending the Seljuk frontier against Byzantine and crusading Christian forces.

Through war and alliances, Osman expanded the reaches of his domain. In 1299, Osman declared independence from the crumbling Seljuk Empire. During his reign, he extended the reaches of his domain from 4,000 to 16,000 square kilometers. Before his death, he would establish a policy of limited religious tolerance that would be a hallmark of the empire.