Kublai was the fourth son of Tolui (his second son with Sorghaghtani Beki) and a grandson of Genghis Khan. He succeeded his older brother Möngke as Khagan in 1260, but had to defeat his younger brother Ariq Böke in the Toluid Civil War lasting until 1264. This episode marked the beginning of disunity in the empire. Kublai's real power was limited to China and Mongolia, though as Khagan he still had influence in the Ilkhanate and, to a significantly lesser degree, in the Golden Horde. If one counts the Mongol Empire at that time as a whole, his realm reached from the Pacific Ocean to the Black Sea, from Siberia to what is now Afghanistan.
In 1271, Kublai established the Yuan dynasty, which ruled over present-day Mongolia, China, Korea, and some adjacent areas, and assumed the role of Emperor of China. By 1279, the Mongol conquest of the Song dynasty was completed and Kublai became the first non-Han emperor to conquer all of China.
Kublai Khan was the fourth son of Tolui, and his second son with Sorghaghtani Beki. As his grandfather Genghis Khan advised, Sorghaghtani chose a Buddhist Tangut woman as her son's nurse, whom Kublai later honored highly. On his way home after the Mongol conquest of Khwarezmia, Genghis Khan performed a ceremony on his grandsons Möngke and Kublai after their first hunt in 1224 near the Ili River. Kublai was nine years old and with his eldest brother killed a rabbit and an antelope. After his grandfather smeared fat from killed animals onto Kublai's middle finger in accordance with a Mongol tradition, he said "The words of this boy Kublai are full of wisdom, heed them well - heed them all of you."
After the Mongol conquest of the Jin dynasty, in 1236, Ögedei gave Hebei (attached with 80,000 households) to the family of Tolui, who died in 1232. Kublai received an estate of his own, which included 10,000 households. Because he was inexperienced, Kublai allowed local officials free rein. Corruption amongst his officials and aggressive taxation caused large numbers of Chinese peasants to flee, which led to a decline in tax revenues. Kublai quickly came to his appanage in Hebei and ordered reforms. Sorghaghtani sent new officials to help him and tax laws were revised. Thanks to those efforts, many of the people who fled returned.
The most prominent, and arguably most influential, component of Kublai Khan's early life was his study and strong attraction to contemporary Chinese culture. Kublai invited Haiyun, the leading Buddhist monk in North China, to his ordo in Mongolia. When he met Haiyun in Karakorum in 1242, Kublai asked him about the philosophy of Buddhism. Haiyun named Kublai's son, who was born in 1243, Zhenjin (Chinese: True Gold). Haiyun also introduced Kublai to the formerly Daoist and now Buddhist monk, Liu Bingzhong. Liu was a painter, calligrapher, poet, and mathematician, and he became Kublai's advisor when Haiyun returned to his temple in modern Beijing. Kublai soon added the Shanxi scholar Zhao Bi to his entourage. Kublai employed people of other nationalities as well, for he was keen to balance local and imperial interests, Mongol and Turk.