Kurulus Osman is a Turkish historical and fiction drama serial. It is made up on the founder of the Ottoman Caliphate Osman Gazi. He was the son of the head of Kayi Tribe Ertugrul Gazi. Kayi tribe migrated to Anatolia from Central Asia. It was the branch of the Oghuz dynasty. All these lands were under the Seljuk Empire. Sultan Alladin Keykubat and Giyaseddin Keyhusrev were the Sultans in that era. Osman became the tribal head after the death of his father Ertugrul Gazi. Kayi tribe was the largest and the powerful Turk tribe. They had borders with Byzantine lands.