The half-brother young Temujin killed after a dispute over hunting spoils was Behter.
After Temujin’s father, Yesugei, died, the family was abandoned by its tribe and forced to survive by fishing, gathering roots, and hunting. Behter, the older son of Yesugei’s secondary wife, had a seniority claim within the fractured household.
Tensions grew when Behter and his younger full brother Belgutei took hunting spoils from Temujin and his younger brother Qasar. Temujin and Qasar ambushed Behter and killed him. Their mother, Hoelun, angrily rebuked them for violating family solidarity.
A common mix-up is Belgutei: he was Behter’s younger full brother, but he survived and later became one of Temujin’s important allies. The episode is chiefly known from the Secret History of the Mongols and is often presented as an early sign of Temujin’s ruthless struggle for authority.