Genghis' childhood name was Temüjin. He had three brothers named Khasar (or Qasar), Khajiun, and Temüge, and one sister named Temülen (or Temülin), as well as two half-brothers named Bekhter and Belgutei. Like many of the nomads of Mongolia, Temüjin's early life was difficult. At nine years old, as part of the marriage arrangement, he was delivered by his father to the family of his future wife Börte, who was a member of the same tribe as his mother. He was to live there in service to Sansar, the head of the household, until he reached the marriageable age of 12. While heading home, his father was poisoned during a meal with the neighboring Tatars, who had long been enemies of the Mongols. Temüjin returned home to claim the position of khan. However, his father's tribe refused to be led by a boy so young. They abandoned Hoelun and her children, leaving them without protection.
For the next several years, Hoelun and her children lived in poverty, surviving primarily on wild fruits, marmots, and other small game hunted by Temüjin and his brothers. It was during one hunting excursion that 13-year-old Temüjin killed his half-brother, Bekhter, during a fight which resulted from a dispute over hunting spoils. This incident cemented his position as head of the household.
In another incident in 1182 he was captured in a raid and held prisoner by his father's former allies, the Bjartskular ("wolves"). The Bjartskular enslaved Temüjin (reportedly with a cangue), but with the help of a sympathetic watcher, the father of Chilaun (who would later become a general of Genghis Khan), he was able to escape from the
ger by hiding in a river crevice. It was around this time that Jelme and Arslan, two of Genghis Khan's future generals, joined forces with him. Along with his brothers, they provided the manpower needed for early expansion. Temüjin's reputation also became relatively widespread after his escape from the Bjartskular.
At this time, none of the tribal confederations of Mongolia were united politically, and arranged marriages were often used to solidify temporary alliances. Temujin grew up observing the tough political climate of Mongolia, surrounded by tribal warfare, thievery, raids, corruption and continuing acts of revenge carried out between the various confederations, all compounded by interference from foreign forces such as the Chinese dynasties to the south. Temüjin's mother Ho'elun taught him many lessons about the unstable political climate of Mongolia, especially the need for alliances.
As previously arranged by his father, Temüjin married Börte of the Olkut'hun tribe when he was around 16 in order to cement alliances between their respective tribes. Börte had four sons, Jochi (1185–1226), Chagatai (1187—1241), Ögedei (1189—1241), and Tolui (1190–1232). Genghis Khan also had many other children with his other wives, but they were excluded from the succession, and records of daughters are nonexistent. Soon after Börte's marriage to Temüjin, she was kidnapped by the Merkits, and reportedly given away as a wife. Temüjin rescued her with the help of his friend and future rival, Jamuka, and his protector, Ong Khan of the Kerait tribe. She gave birth to a son, Jochi, nine months later, clouding the issue of his parentage. Despite speculation over Jochi, Börte would be his only empress, though Temüjin did follow tradition by taking several morganatic wives.