Killua is a member of the Zoldyck family, who are all legendary assassins. Since birth, he trained endlessly in the art of assassination. He eventually ran away from his family and profession to participate in the Hunter exam. He befriended Gon almost immediately and has loyally followed him since then. Killua is usually a kind-hearted and playful boy, but once provoked he becomes extremely violent and bloodthirsty. This seems to be a trait he got from his father, who believes that Killua would eventually return home as an assassin. He is also a transmuter and constantly strives to improve his nen ability, developing many interesting techniques as the show progresses.
