Ertuğrul (Ottoman Turkish: ارطغرل, often with title Gazi) (1191/1198 Ahlat – 1281 Söğüt) was the father of Osman I, the founder of the Ottoman Empire. He was the leader of the Kayı clan of the Oghuz Turks. When arriving in Anatolia with his 400 horsemen to aid the Seljuks of Rum against the Byzantines, Ertuğrul set off the chain of events that would ultimately lead to the founding of the Ottoman Empire. Like his son, Osman, and his future descendants, Ertuğrul is often referred to as a Ghazi, a heroic champion fighter for the cause of Islam.

In 1227, he inherited the command of the Kayı tribe of the Oghuz Turks as a result of his assistance to the Seljuks against the Byzantines. Ertuğrul received lands of Karaca Dağ, a mountainous area near Angora (now Ankara), by Ala ad-Din Kay Qubadh I, the Seljuk Sultan of Rum. One account indicates that the Seljuk leader's rationale for granting Ertuğrul land was for Ertuğrul to repel any hostile incursion from the Byzantines or other adversary. Later, he received the village of Söğüt which he conquered in 1231 together with the surrounding lands. That village became the Ottoman capital in 1299 under Osman I, Ertuğrul's son. Ertuğrul had two other sons, Savdji and Gündüz.