Osman I (1259-1326) was the leader of a tribe of conquering warriors, who formed an independent state out of which arose the great Ottoman Empire.

Born in 1259, Osman I entered a world desperately in need of a leader. In Eastern Europe and the Middle East several great empires were declining. The Byzantine Empire—the eastern Roman Empire based around the capital city of Constantinople (Istanbul)—had endured for nine centuries but was beginning the long process of decline. During the Fourth Crusade of 1204, Constantinople fell for the first time to the Latin knights of the crusade. Impregnable, due to its strategic geographic position and defenses, the fall of the capital city symbolized the declining power of the Byzantine emperor. On the eastern flank of Byzantine lay the Seljuk Empire, consisting of eastern Asia Minor, Syria, Mesopotamia, Armenia, part of Persia, and western Turkestan. But this Empire too began to lose control of its possessions due to the invasions of mongol leader Genghis Khan.

After the decisive battle of Kozadagh ended with victory for the Mongol invaders, the Seljuk sultans were reduced to vassals. The Mongol khan, interested only in securing annual payments from his vassal states, did not implement a system of control and government over the former Seljuk territories. With Byzantine control diminishing, Seljuk rule subjugated, and Mongol leadership missing, a power vacuum resulted in Asia Minor.

Situated on the border between the Byzantine and Seljuk empires was a frontier area inhabited by a collection of nomads and city dwellers of many races and religions. Driven up from the east due to political turmoil and the advancing Mongol hordes, many were of Turkoman descent. Caught between feuding and declining empires this area had all the characteristics of a frontier. Beyond the limits of central control, power rested in the hands of independent Ghazi leaders who ruled over small tribes and parcels of land. These Ghazis were Turkish warriors fighting for the faith of Islam against the infidel, the Christian settlers in Byzantine areas. On horses, the Ghazis raided and looted Christian villages, securing the goods on which their wealth was based.

One of these leaders was Ertogrul, the father of Osman. There are conflicting stories as to the origin of the Ottomans and their arrival in the frontier area of Anatolia. The most common story is that Ertogrul's father Suleyman Sah, the leader of a tribe of Turkomans, led his people out of northeastern Iran in the late 12th century, just ahead of a Mongol invasion. Fearing death or enslavement, they headed west where Suleyman is said to have drowned crossing the Euphrates. Assuming the leadership, Ertogrul led part of the tribe into Anatolia where they settled. Older versions of the story are more detailed but unsubstantiated.
Historian Edward S. Creasy relates that Ertogrul and his small band, while journeying westward into Asia Minor, came upon two armies engaged in battle. Seeing that one army was much larger than the other, Ertogrul and his followers entered the fray on the side of the smaller force without knowing for whom they fought. Their addition made the difference and the smaller force was victorious. Once the battle was over, Ertogrul learned that the leader of the small force was Alaeddin, the Seljuk sultan, and the army defeated were Mongol invaders.

In gratitude, Alaeddin bestowed on Ertogrul a principality on the frontier, bordering the Byzantine state. Regardless of the truth of this part of the story, there is no doubt that Ertogrul was given his fief in the area of Sogut in northeast Anatolia (roughly, present-day Turkey) to act as a guard and defender of the Seljuk border against the Byzantine forces. In the spirit of a true Ghazi, Ertogrul performed this job for the remainder of his life; he did not acquire any territory beyond the land given him. When he died in 1288, he left his fief and tribal leadership to his son Osman.

Born in 1259 at Sogut, few personal details of Osman's life exist. Legend has it that as a young man, he fell in love with Malkhatun—which apparently means "Treasure of a Woman"—and asked to marry her. But her father, a renowned holy man, refused. Resigned to unhappiness after several more years of refusal, Osman had a dream; he saw himself and a friend sleeping. From his friend's chest arose a full moon (symbolizing Malkhatun) which moved over and sank into the chest of Osman. From this union sprang a great tree which grew, eventually encompassing the world. Supported by the four great mountains—Caucasus, Atlas, Taurus, and Haemus—the tree covered a world of bountiful harvests and gleaming, prosperous cities. Then a wind began to blow, pointing all the leaves of the tree towards Constantinople. As Edward Creasy describes the rest of the dream:
That city, placed at the junction of two seas and two continents, seemed like a diamond set between two sapphires and two emeralds, to form the most precious stone in a ring of universal empire. Othman thought that he was in the act of placing that visioned ring on his finger, when he awoke.

This dream, so obviously a prophesy of a great and powerful empire that would result from a union of Osman and Malkhatun, caused Malkhatun's father to recant and agree to the marriage. Although this story of Osman's vision of empire is probably only a legend created through hindsight, Osman and his descendants did, indeed, create an empire.

By the time Osman assumed the leadership of his father's tribe in 1288, the stronger Ghazi leaders had begun, through conquest, to form larger principalities. Unlike his father, Osman too began a campaign of conquering the neighboring towns and countryside. In 1299, he symbolically created an independent state when he stopped the payment of tribute to the Mongol emperor. From 1300, there was a period of sustained conquest as he acquired the land west of the Sakarya River, south to Eskishehir and northwest to Mount Olympus and the Sea of Marmara. Osman and his men captured the key forts and cities of Eskishehir, Inonu, Bilejik, and eventually Yenishehir where he established a capital for the new Ottoman state. Still, they were not strong enough to capture the crucial and strongly fortified cities of Bursa, Nicaea, and Nicomedia.

On reaching the Sakarya River and the Sea of Marmara by 1308, Osman had effectively isolated the city of Bursa. An important Byzantine center at the foot of Mount Olympus, Bursa was well fortified, surrounded by a high wall and several small forts and outworks. With all the land around it occupied by Osman, Bursa was still able to receive supplies and communication through the port of Mudanya. Since Osman's troops could not take the city by force, Osman put Bursa under siege to force a surrender. Then in 1321, Osman took the port of Mudanya, thereby effectively isolating Bursa's inhabitants from the outside world. Incredibly, the siege went on for five more years, the city's stubborn inhabitants refusing to surrender. Inevitably though, the city fell, surrendering to Osman's troops on April 6, 1326.
The surrender of Bursa marked a turning point in the development of Osman's new state. Although Osman had been rapidly acquiring land since 1288, the acquisitions were mainly rural with nomadic peoples. Bursa was a major commercial center which opened up the new state to the rest of the world. From that point on, the Ottoman state was an important player in the events and decisions affecting the Middle East and Eastern Europe.

The year 1326 also marked a turning point with the death of Osman. Due to age and increasing illness, he had placed his eldest son Orhan at the head of his troops. On his deathbed at Sogut, Osman lived long enough to hear from his son of the surrender of Bursa. According to legend, Osman then gave Orhan his final advice:
My son, I am dying; and I die without regret, because I leave such a successor as thou art. Be just; love goodness, and show mercy. Give equal protection to all thy subjects, and extend the law of the Prophet. Such are the duties of princes upon earth; and it is thus that they bring on them the blessings of Heaven.
In recognition of the importance of the victory, Osman then directed Orhan to bury him at Bursa and to make it the capital city of the new Empire. Shortly after, Osman died at the age of 67. As requested, he was buried at Bursa in a beautiful mausoleum which was to stand as a monument to him for several centuries after.

Unlike his father before him, Osman bequeathed to his son an independent state. It is uncertain whether the minting of coins and the pronouncement of prayers to the house of Osman, the signs of independence, began in the last years of Osman's rule or in the beginning of Orhan's. Still, by the time of his death, Osman had created a state independent of either Byzantine or Mongol control. Recognizing the weakness of the Byzantine Empire, Osman had directed his efforts to acquiring territory at the Byzantine's expense. Crucial to his success was his ability to attract other Ghazi warriors to fight under him. Motivated to fight against the infidel, these Turkish nomads were attracted to Osman's conquest of the Christian towns and cities. Most authors speak of the loyalty and devotion that Osman was able to command from his men.
As a ruler of the people in his dominions, as well as of his troops, Osman had received loyalty and respect. He was reputed to be just in his decisions and in his treatment of all people. All citizens, regardless of ethnicity or religion, were treated equally with respect to property and person. Yet, Osman could also be ruthless in demanding obedience from his followers. One story, whose validity cannot be assured, relates the situation surrounding Osman's decision to attack an important Greek fortress. Osman's uncle, Dundar, who reportedly had been one of the original settlers in Sogut after crossing the Euphrates, opposed the attack as too risky. Perceiving his uncle's actions as a threat to his authority as well as to his rule, Osman said nothing but, raising his bow, shot and killed his uncle instantly. Like his successors, Osman expected obedience and respect from his subjects and soldiers.

Following in his father's footsteps, Orhan continued to expand the new state into Byzantine territory, capturing the cities of Nicaea in 1331 and Nicomedia in 1337. By 1345, the Ottoman state had grown significantly, encompassing all of northwestern Asia Minor from the Aegean to the Black Sea. This expansion was to continue until the late 17th century. From modest beginnings, Osman created the basis for one of the largest and longest-lived empires ever. By 1683, the Ottoman Empire encompassed the Balkans, Greece, Hungary, and Italy in the west, the north shore of the Black Sea, the entire Middle East, Egypt and parts of Arabia along the shores of the Red Sea, as well as all of North Africa, and parts of Morocco and Spain. Although expansion ended after 1683 and decline began, the Ottoman Empire continued to exist until the first World War. Enduring for over 600 years, Osman's state had an enormous effect on the course of historical events in Europe, Asia, the Middle East, and Africa. It is as the founder of this great Empire that Osman acquires his fame.