Osman I was born around 1258 in the region of Bithynia, in modern-day Turkey. He was the son of Ertuğrul Bey, the leader of a small group of Turkish tribes. This was a period of significant turbulence and change, marked by the decline of the Seljuk Sultanate of Rum and the rising threat from the Mongols. As a young leader, Osman inherited not just territory but also the ambitions to expand and unify the Turkish tribes in the region.