Killua was born as the middle child to a family of known assassins, the Zoldycks. Showing great promise from birth, Killua followed the traditional Zoldyck training. He had already mastered many killing techniques at a tender age, and was set to be one of the best assassins the family has ever produced. At the age of three, he started his training on tailing other people. He was forced to battle in the Heavens Arena martial arts tournament at the age of 6, in which he took two years to get to the 199th floor (even though he was accepted to the 200th floor, he bailed out). Killua divulges that ever since his birth, he has been in constant training for the occupation of a professional assassin. Killua had spent years trying to perfect unique skills that assassins portray and possess.
Bored and tired of killing, Killua unexpectedly rebelled against his family. Injuring both his mother and second brother, and ran away from home to take the Hunter Exam for fun. He meets Gon during the first portion of the Hunter Exam, and they become the best of friends. He thinks being with Gon is exciting and adventurous.
Initially, Killua is introduced as a character who appears similar to Gon, but different at the same time; cheeky, cheerful, and full of mischievous ideas. He is also one of the quickest-thinking characters in the series and often analyzes a situation with great ease and accuracy. In spite of his young age, his way of thinking, knowledge, and pragmatism give him the attitude of an adult. He is confident in his own abilities, often being humble about it; but when somebody compliments him, especially Gon, he becomes easily embarrassed. Killua is also known for having a sweet tooth; he loves everything sweet and spent almost 200 million Jenny on snacks when he was at the Heavens Arena. His favorite snack is chocolate, specifically Chocolate Balls.
However, his ruthlessness and aptitude in killing shows the other side of him — deadly, violent, and bloodthirsty. Conflicting with Killua's predisposal to kill is his unyielding loyalty to his friends and natural kindness. He claims Gon was his first friend, and he grows progressively more attached to him as time passes. Killua often suffers immensely in his attempts to help his friends without a single complaint. He puts others before himself without being concerned about his own health or even his life.
Until recently, Killua's greatest flaw was his fear of those seemingly more powerful than him (one of whom being his elder brother, Illumi). Killua had been trained as an assassin by his brother to be extremely cautious that he only engages in combat provided that victory is absolutely certain. This impeded him as a Hunter, as Biscuit stated more than once that victory is never certain, and that depending on the circumstances, a person has the potential to defeat a stronger opponent.
Killua especially struggles with these dueling ideologies during the latter half of the series, as he begins to encounter stronger opponents. His brother's teachings remained firmly entrenched in his mind, to a point at which Biscuit prophesied that he would one day abandon Gon because of this. Biscuit gave Killua an ultimatum: Defeat Shoot to claim the right to go with Gon and fight the Chimera Ants or in case Killua lost, he resolved to leave after Gon had recovered from his fight, protecting him in the meantime.
Finally he had to face Biscuit's prophecy when he encountered a Chimera Ant while Gon (who could not use Nen at the time) was not far off and had no way to defend himself. Killua made an attempt to save Gon. While fighting with the Chimera Ant, Killua was also battling his inner self. Preoccupied, Killua was losing to the Chimera Ant. At the last moment, Killua realized that Illumi had implanted a needle in his brain way back in the first Hunter Exam. This needle was responsible for forcing Killua to retreat and jailing himself in his comfort zone whenever any situation would potentially endanger his life. Upon extracting the needle, Killua was freed from this restraint and gained full control of his subconscious to make his own decision whether or not to flee whenever there is a need to fight stronger opponents.
He has white hair, pale skin, black thick eye brows and black eyes. He wears a white t shirt and a black turtleneck. He wears black shorts along with long socks and sneakers.
Killua has spiky silver hair, very pale skin and blue eyes. His eyes change shape depending on the mood that he's in, narrowing and sharpening when he goes into assassin mode. Killua is fairly lean at the start of the series, due to constant physical conditioning and torture training he received when he was young. As time passes, he becomes more muscular and toned. In the Nippon Animation anime adaptation, Killua's eye color is changed to green during the OVAs. He is also often seen holding a green skateboard (turned yellow in the 2011 series).
Killua typically wears baggy clothing, with his usual attire consisting of long-sleeved and dark-colored shirts. Most of his clothes have a turtleneck. Killua wears long, baggy shorts in the manga and Madhouse animated adaptation, but Nippon Animation's character design shortened them to reach above his knees. Killua also wears blue boots, recolored brown and black in the 1999 anime.
As a child, Killua's hair is longer, almost cascading to his shoulders. He wore a hoodie with his trademark blue coloring, grey pants, and shoes.
Hunter X Hunter (Anime)
- Maha Zoldyck (Great-Great-Grandfather)
- Great-Grandmother (status unknown)
- Zeno Zoldyck (Grandfather)
- Grandmother (status unknown)
- Kikyo Zoldyck (Mother)
- Silva Zoldyck (Father)
- Illumi Zoldyck (Older brother)
- Milluki Zoldyck (Older brother)
- Alluka Zoldyck (Younger sibling)
- Kalluto Zoldyck (Younger brother)
- Japanese : Kanako Mitsuhashi (1999 series), Mariya Ise (2011 series)
- English : Annika Odegard (1999 series), Cristina Vee (2011 series)