Although he was the least mentioned prince by medieval historians, Genghis Khan's youngest son Tolui is thought to have had the most influence among the sons of Genghis Khan on the growth of the empire with his activities during his life and legacy he left behind after his death. Tolui, the last son of Genghis Khan born from Genghis Khan's chief wife Borte Ujin, has six wives including his chief wife named Sorghaghtani Beki, ten sons, three daughters and hundreds of grandchildren. Tolui did not gain the title of Great Khan, although he was a regent for two years between 1227 and 1229 following the death of Genghis Khan. After his death, however, his children became the absolute rulers of nearly the entire Mongol Khanate within thirty years. He was the father of three great figures, Mongke, Kublai and Hulegu, two of whom had obtained the throne of the dependent Mongolian State, the other obtained the great Khanate in Karakorum, and directly influenced the political life of the Mongols. However, Tolui's stepchildren Moge, his grandchildren Toq Temiir and Kelmish Aqa, who were born from other wives and concubines, had strong influence in the domestic and foreign politics of the Mongols. Chief Khatun Sorghaghtani Beki, who was indiscriminately interested in their education, had an important role in raising all the legal and stepchildren of Tolui as qualified rulers in addition to the inheritance left to them. In this study, which is the first part of a series of articles consisting of three studies, we attempted to introduce Tolui family in integrity as well as explaining its effects on Mongolian domestic and foreign politics