Osman Gazi was only 23 years old when he took the control of Kayi Clan in Sogut and than ascended the throne after the death of his father, ruling for 27 years until his death in 1326.

After his ascension to throne, he gathered several Turcoman groups around himself and fought against Byzantines, collaborating with Alaeddin Keykubad I of the Seljuks. When the Seljuk Empire remained rulerless after the exile of Alaaddin, Osman Gazi reunited them under his rule in 1299 marking the history as the foundation of the Ottoman Empire.

Osman Gazi continued his campaigns against the remaining Byzantine Empire in the area along with his brothers, sons, and close supporters. He cut the Byzantine trade routes forcing local rulers to surrender. After 1320 he got sick so his sons continued to fight, capturing many towns from the Byzantines. He died of gout at the age of 68 in Sogut and buried in the city of Bursa.

During his rule, he married Mal Hatun first, from which he had a son, Orhan Gazi who later became the next sultan. After Mal Hatun he married Bala Hatun from which another son, Alaaddin was born who became his Grand Vizier when grown up. He had a total of 8 sons and 1 daughter.

Osman Gazi was nicknamed as Black (Kara in Turkish), which according to an ancient Turcoman tradition signifies brave and heroic person. He was a tall man with a broad and high chest and long arms, dark tan, round face with a thin beard and long thick mustache, ram-nose, hazel eyes, thick eyebrows, had deep and fine voice, expert on horse riding, sword using, and battle strategies. He was fair, helped very much to the poor people, even giving them his own clothes if he saw a person in need.

Besides military actions, Osman Gazi also established all new measures to form a new empire, such as bringing new laws based on Seljuk laws as well, adopting taxes, minting the first Ottoman coins (Akçe), and so on.

Osman Gazi appreciated the opinions of Edebali (the famous Ahi Sheik) and he respected him. He often went to Edebali's house where a dervish group meets in Eskisehir Sultanonu and been his guest.

One night, when he was a guest in Sheik Edebali's dergah, he had a dream. As the sun shined, he went to Edebali and told him: "My Sheik, I saw you in my dream. A moon appeared in your breast. It rose, rose and then descended into my breast. From my novel there sprang a tree. It grew up and turned green. It branched out and got complicated. The shadow of its branches covered the whole world. What does my dream mean?

After a little silence, Seyh told him:
I have got good news Osman! God gave you sovereignty and to your son. All the world will be under the protection of your son and my daughter will be the wife to you."

After this unusual event, the Sheik gave his daughter Bala Sultana to Osman and Alaeddin was born from this marriage.Upon his conquest of the fortress of Bilecik, Alaeddin Keykubat, who is the ruler of the Seljuks of Rum, sent him "a horsetail, a standard and a drum" as the insignia of sovereignty in 699 A.H. (1299 A.D.). Thereupon, he minted coins and had the Friday prayers recited in his name alone. His grand vizier was his younger son, Alaeddin Pasha. Osman was the first to Ievy a tax of one "akçe". Osman Gazi was surnamed "Black", which according to an ancient Turcoman tradition signifies brave and heroic. As we learn from the Oðuzname, the same epithet was given to Kara Yusuf, the ruler of Karakoyunlus, and to Kara Yülük Osman Bey, the Sultan of the Akkoyunlus.
The founder of Ottoman empire- risen from Anatolia and reigned for 600 years, over three continents- Osman Gazi, died of gout, in Bursa in 1326. When he died, he left an horse armor, a pair of high boots, a few sun jacks, a sword, a lance, a tirkes, a few horses, three herds of sheep, salt and spoon containers.

His Wifes : Mal Hatun , Rabi'a Bala Hatun
His Sons : Pazarli, Coban, Hamit, Orhan, Ala-ed-din, Ali, Melik, Savci
His Daughters : Fatma Sultan