Age: 12 (beginning), 15 (current)
Birth date: July 7
Height: 158 cm
Weight: 45 kg
Eye color: Deep teal (1999), Royal blue (2011)
Blood type: A
Occupation: Assassin, hunter
Nen Type: Transmutation
Killua is a member of the Zoldyck family, who are a family of legendary assassins. Since birth, he trained endlessly in the art of assassination. He eventually ran away from his family and profession and joined the Hunter exam. He befriended Gon almost immediately and has loyally followed his best friend 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 trait would eventually make Killua return home.
He is also from the transmutation nen group. He constantly strives to improve his nen ability, developing many interesting techniques as time moves on.