Sasuke was born into the Uchiha clan of Konohagakure, the younger son of the clan's head, Fugaku, and his wife Mikoto. His older brother Itachi was a prodigy the whole village watched, and Sasuke spent his early years trying to be seen the way Itachi was seen.
That childhood ended in one night. Itachi killed every member of the Uchiha clan, their parents included, and left only Sasuke alive. He told his younger brother to hate him, to hold onto that hatred, and to grow strong enough to one day take revenge. Sasuke was a child when he was handed that instruction, and he built the rest of his childhood around it.
He stayed in Konoha and returned to the Academy, but he kept his distance from everyone around him. Classmates read him as cold and arrogant. What they were seeing was a boy who had decided that bonds were a distraction from the single task that mattered. He called himself an avenger.