The founder of Ottoman Empire was Osman Ghazi. Osman Ghazi was born in 1259 in the city of Sogut. He was on of the three sons of Ertuhrul Ghazi and Halime Hatun. Osman Ghazi was only 23 years old when he became the bey of Kayi tribe. After the death of his father, he ascended the throne and ruled for 27 years until his death in 1326.

After he ascended the throne, he gathered many Turkmen groups and fought against Byzantine groups with Seljuk's Alaedin keykubad 1. When the ruling of Seljuk Empire came to an end, they broke into pieces. Osman Ghazi reunited them under his rule and established world largest empire, The Ottoman Empire.

During his rule, he married Malhun Hatun, from he had a son, Orhan Ghazi who became the next sultan. After Malhun Hatun, he married Bala Hatun, from which he had second son, Alaadin who became Orhan's grand vizier when he grown up. Osman Ghazi had 8 sons and 1 daughter.

Osman Ghazi continued his campaigns against remaining Byzantine empire with his sons, brothers and close supporters. He cut many byzantine trade routes and force the local leaders to surrender. After 1320, he got sick so his sons continued to fight and conquered many towns from byzantine empire. He died of gout at the age of 68 in Sogut and buried in the city of Bursa.

Osman Ghazi was nicknamed as black (Kara in turkish) according to Turkmen traditions means brave and heroic people. He was a man with broad and high chest, long arms, dark tan, thin beard and long thick mustache, ram nose, hazal eyes, had deep and fine voice, expert on horse riding, using swords and battle strategies. He was fair, helped the poor very much and if a person is in need, he even give his own clothes to them.

Osman Ghazi also established mew measures to form a new state, bringing new laws including Seljuk laws. He adopted taxes, minting the first Ottoman coins(Akce) and so on. Then Orhan Ghazi and his lineage ruled over three continents for six hundred years bearing the name if Osman Ghazi as The Ottomans.