Ertuğrul (Ottoman Turkish:ارطغرل‎, often with the title Gazi) (1188/1191/1198 – 3 May 1281) 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 from Merv (Turkmenistan) 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.