One of the breaking points in Turkish and Islamic history is the Battle of Dandanakan, which took place between the Seljuks and the Ghaznavids in 1040. After the war, the Seljuks became an effective and decisive power, especially in the Sunni Islamic geography with a rapid rise. The Great Seljuk Empire, which came from a nomadic culture and irrepressibly expanded its domination from Turkistan to Anatolian territory in a very short time while it was in the nature of a nomad group, started to mature institutionally as well. At this point, the Persian origin statesmen, many of whom previously served in the state organization of Ghaznavid, met the need for trained personnel that emerged both in the central government and in the provinces. One of these names is Hasan b. Ali b. Ishaq al-Tusi, who will become famous with the name of Nizam al-Mulk and will get ahead of his original name. Nizam al-Mulk has been an extremely effective name in the institutionalization of the Great Seljuk State with the steps and actions which he tookin the military, administrative, scientific, and economic fields at a time when the state power was depended on victories in the military field. As a result of that event, he gained a respectable place among both public and statesmen. Within the scope of this study, the position of Nizam al-Mulk in the state bureaucracy, his relations with the rulers and dynasty members, and the reflections of the actions taken by him from his period of vizier to the Seljuk history will be discussed. Nizam al-Mulk, who started to work in admistrative services of the state alongside of Ebu'l-Fazl Suri who was the governor of Ghaznavids in Khurasan, continued his services in the Seljuk State after Khurasan passed under the control of Seljuks. Nizam al-Mulk proved his capacity to Cagri Beg and then he became one of the most trusted names of Cagri Beg. Thus, Cagri Beg assigned his son Alp Arslan, who will take over the administration of Khurasan first, and then the entire Seljukid regions, and advised his son to consider Nizam al-Mulk as a father and not to go against him. Alp Arslan appointed to Nizam al-Mulk as vizier, the most important administrative duty of the state, because of the advice of his father and the contributions of Nizam al-Mulk, in the struggle of Alparslan for sultanate throne against his half-brother Sulaiman. From this period until his death, Nizam al-Mulk was the vizier of the Great Seljuk State for about 30 years without interruption and became the most influential figure of the Great Seljuk politics since the second half of the 5/11th century. Although the belief is that the sultan who is a person chosen by God to rule the earth, the sultan considered the vizier blessing, and his thoughts with regard to the vizier was positively affected by some reasons such as the link to the dethroning of Malikshah, his success in the state goverment, the regulation of the state system, the development of the cities and the strengthening of the economy, and the abilities of Nizam al-Mulk. One of the points that should be emphasized at this point is how Nizam al-Mulk saw himself and where he put his position in the state. Nizam al-Mulk, in a reply to Sultan Malikshah, linked the presence of the state and the sultan with his own existence. Thus it shows that Nizam al-Mulk who is one of the most talented viziers in the history is highly self-confident and sees himself as a powerful person. This situation causes to question the source of the power the fact that a person who does not have any blessings among the public challenges to the sultan who is believed to have been chosen by God in society. The sought answer is found in the determination of the process of Nizam al-Mulk's as vizier under various headings giving certain examples that indicates his effect on the interior functioning of the state and in his relationship with different segments. Nizam al-Mulk had a close relation with the Seljukian throne. Thus, he showed his relation in every necessary cases by colliding in the battlefield, solving the problem of the government with his agile intelligence before becoming dangerous for the state, and providing the growth of the state with his political prediction and contributions. His loyalty and sincerity were not unreciprocated by the Seljuk sultans. Even Alparslan gave great importance to the ideas of the vizier, he shaped his preferences according to him, and he ignored any word against Nizam al-Mulk. Accordingly, Malikshah showed sincere respect to Nizam al-Mulk, who gave him the Seljukian throne, assigned him as the execution of all state affairs, and considered him as a "father". In addition, Malikshah gave the title of atabeg (al-amiru'l-valid) to Nizam al-Mulk as the first in Seljuk history. Malikshah spent his first years of the sultanate of the Great Seljuk by playing polo and holding big hunting parties with the influence of youth, and therefore, all power within the state passed into the hands of Nizamulmulk. This emerging situation, is explained with the statement: "Although the country was officially and namely belong to the sultan, in reality, it was ruled by 'Nizam'. " Also, the military, political, and economic successes achieved during the reign of Malikshah were attributed to Nizam al-Mulk's talent and actions in state affairs. Nizam al-Mulk, who had a strict relationship with the dynasty, also developed a close relationship based on trust with different entities who took office at the administrative service. For example, in the military campaigns in which Nizamulmulk participated, the participation of Nizam al-Mulk among soldiers like a soldier in the war led to respect towards Nizam al-Mulk in the army. In addition, Nizam al-Mulk prevented the emergence of support letters written by some names for the benefit of Kawurd Beg in the struggle between Malikshah and Kawurd Beg who was the power in Kirman for the throne. Therefore, this case increased his reputation among amirs. Another group in which Nizam al-Mulk was in close contact became the class of science. Nizam al-Mulk allowed scholars who were oppressed by Amid al-Mulk al-Kunduri during the period of Tughril Beg to return to their homes. These scholars always allocated a special place in their minds and hearts to the names that provide them return to their homes. The dedication of their works to Nizam al-Mulk was an indication of this. Taking a step further, Nizam al-Mulk constructed madrasas over the cities of the state for these scholars, with the permission of Sultan Alparslan and Malikshah. In these madrasas, which were named as Nizamiyya madrasa in the name of Nizam al-Mulk, the opportunities offered to students both during the education period and after their graduation increased the interest of people in madrasas. While a debt was paid to the scholars who were displaced and oppressed by means of madrasas, a qualified manpower required by the administrative and judicial system of the Great Seljuk State was grown, on the other hand. Nizam al-Mulk provided the support of the public with the actions that he took in favor of the society and gave importance to the solution of the problems. It was emphasized that people were grateful to him throughout their lives. Nizam al-Mulk paid attention to the solution of the problems of the people and took care of them closely. The feeling of trust given by Nizam al-Mulk had been appreciated by public and allowed him to be accepted by public. Another feature of Nizam al-Mulk was helping poor people and sitting with them in the same food table. Thus, he would have a dialogue with them and gain their appreciation. Nizam al-Mulk, who was a complete statesman in all aspects, considered the solution of every need of the society, and took actions in this direction. The sincere and close relationship that Nizam al-Mulk established with every segment of the society that it allowed Nizam al-Mulk received such a great appreciation and was regarded like a sultan by the society. In addition, it was compared to the Kaaba because of the fact that people from all over the Seljuk geography and from all segments of the society turned to Nizam al-Mulk. Nizam al-Mulk became a focus of power with family members working at the administrative services, scholars with whom he was related, army, and governors. As a result, Nizam al-Mulk became the most influential figure of the Great Seljuk politics, the name that determined the Seljuk administration and policies in the last quarter of the 11th century, and he was the decision maker in the most important events of the Seljuk history and ultimately marked the history of the Seljuks. Ibn al-Athir recorded the countless nicknames used by Fatimid vizier Badr al-Djamali, and then, he said: "If the vizier of a state that ruled Egypt only used so many nicknames, Nizam al-Mulk would have made the claim of being the 'deity'. " These words show the power of Seljuks and the situation of Nizam al-Mulk in the Seljuk State.