He is one of the three Heavens Arena fighters who wanted to challenge Gon and Killua for easy wins. He appears to be mean and will do everything in order to become a Floor Master. In the past, he has reached the 200th floor as a rookie without the use of Nen, later was "initiated" after being attacked with a malicious aura attack and lost his left arm. One of Sadaso's dirty tricks was to kidnap Zushi with his Nen hand to threaten Gon to join a match with him. However, Killua learns of the fight between the two and makes a threat against Sadaso's life, frightening him enough to leave Heavens Arena for good. It still remains unknown whether if Sadaso wears a mask or not, which is commented by a ticket seller when he was talking to Killua. When he leaves Heaven's Arena after Killua's threat, he is wearing sunglasses for the first time and his face looks less pale than before. At this point, when he is leaving Heavens Arena, he calls Gido to warn them that Killua will come after them next.
Zeno Zoldyck (ゼノ�ゾルディック Zeno Zorudikku) is Killua's grandfather and Silva's father. A witty old man, his advancing age has not dampened his quick thinking and speed in battle. Zeno wears alternating signs on his garb that say either "A Kill A Day" or "Never Retire." He appears to be on good terms with the Hunter Committee's Chairman, Netero, who hired Zeno to assault Ming Jol-ik's palace in East Gorteau in order to catch the chimera ant King off guard. Zeno favors Killua more than his other grandchildren, most likely because Killua is the heir of the family. Source: HunterXHunter.wikia
Silva is Killua's father. A silent, pensive figure, Killua's interaction with him seems not to be much. He allows Killua to go along with Gon on their journey, but this is only so Killua will gain more experience when thrown out into the real world on his own. During the September third portion of the York Shin City arc, Silva and his father Zeno are both hired by the Mafia to assassinate the Genei Ryodan, but withdraw from the job when their clients are murdered by Illumi, Maha, and Karuto.
Canary is a servant to Zaoldyeck. She may not realize it but she is Killua's friend. She thinks that there difference in status means that they can not be friends. Gon asked her why she had Killua's skateboard. She answered the first time that it was a gift. Later, she tells us he had dropped it. She has a flash back about the tiny skull in her staff. He tries to to give it to her but she refuses it. Then, he tosses it and it lands at her feet and he runs off.
Shachmono is one of Neon's bodyguards. He is one of the two spies in Kurapika's test. Shachmono is a professional hunter. He is from the Emission group. His hatsu is the ability to summon 11 assassin's made out of nen. They can wander only several meters and only respond to simple commands.
Seaquant is a Blacklist Hunter and a servant of the Zoldyck Family. Three years before the beginning of the story, he and 100 henchmen came to attack the Zoldyck estate in Kukuroo Mountain, but they were annihilated by Canary, a mere 10 year-old female trainee butler at that time. Greatly shocked, he begged to become a servant of the Zoldycks. He is now good friends with Zebro, the old groundskeeper of the Zoldyck Family. Seaquant first appears when Gon, Leorio and Kurapika are trying to find a way to meet Killua in the Zoldyck Family's estate. He and Zebro allow the trio to stay in their house and train with their heavy equipments until they are strong enough to open the Testing Gate. After the death of Chairman Netero, he appears at the Hunters Association's headquarters to participate in the election for the 13th Hunter Chairman.