Ertuğrul or Ertuğrul Ghazi was a 13th-century bey, who was the father of Osman I. Little is known about Ertuğrul's life. According to Ottoman tradition, he was the son of Suleyman Shah, the leader of the Kayı tribe of the Oghuz Turks. These Turkomans fled from western Central Asia to Anatolia to escape the Mongol conquests, but he may instead have been the son of Gündüz Alp. According to this legend, after the death of his father, Ertuğrul and his followers entered the service of the Sultanate of Rum, for which he was rewarded with dominion over the town of Söğüt on the frontier with the Byzantine Empire. This set off the chain of events that would ultimately lead to the founding of the Ottoman Empire.

Halime Hatun was, according to Ottoman folklore, the wife of Ertuğrul and the mother of Osman I.