Ertugrul Ghazi is the father of the founder of the Ottoman Empire, Osman Ghazi. Although the information about him is uncertain, it is known that; he was a member of the Kayi Clan. The ancestors of Ertugrul Ghazi were under the command of Sultan Tugrul Bey of Seljuks and Alparslan and they came to Ahlat region first. They joined to the raids in Anatolia. After Eyyubies had captured Ahlat, Gunduz Alp, the father of Ertugrul Ghazi, migrated to Mardin region. And after the plunder of Mardin by the Mongolians, they left this region and they moved through central Anatolia. The Kayi Clan, under the command of Gunduz Alp migrated to Surmelicukur of Pasinler plain of Erzurum. In a short while Gunduz Alp fallen ill and died and Ertugrul Ghazi replaced him. As the Mongolians advanced in Anatolia, he and his brother Dundar Bey moved through the western parts of Anatolia. In Sivas, they assisted the Seljuk Army against the Mongolians. Alaeddin Keykubat, the sultan of the Seljuks rewarded Ertugrul Ghazi for his service and he gave Ertugrul Ghazi, Karacadag and its province, near Ankara. The Kayi Clan had settled in Karacadag for some time, and later they moved through the Sogut region, in the Byzantine border. He campaigned the Byzantine villages. Ertugrul Ghazi helped Alaaddin Keykubat in the war against the Greek Empire in Emeniderbendi (the region between today’s Pazaryeri and Bozoyuk). The sultan gave him Eskisehir and its province to Kayi Clan. After this success, he marched through the Byzantine borders and conquered Sogut. Sogut became the capital of the Kayis. The campaigns continued and Ertugrul Ghazi gained power and extended his borders.