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.
Examinee #384 during the Hunter exam. He is adept in hunting down animals, and is a frequent candidate for the Exam. His weapon is a blowpipe with darts laced with a neurological poison that immobilizes victims. He can track down his victim and lie undetected in the shadows, until opportunity strikes before he makes the deadly move. Gon was the unfortunate victim in stage 4, and had his number tag taken from him. Even more unfortunate was the eventual fate of Geretta, who was killed by the hands of Hisoka during one of his moments of bloodlust.
One of the second stage examiners during the Hunter exam, along with Menchi. Buhara is an epicurean hunter, and is a hulking figure with a large potbelly and an even larger appetite. Buhara's easy-going nature contrasts with Menchi's highly selective one.
Lippo is the proctor over the third and fourth phases of the Hunter Exam: the Trick Tower and the manhunt on Zevil Island. As a prison warden, Lippo concocts devious ideas that test the candidates in different aspects of group dynamics, both in a communal and individual front. Many candidates are forced to work together to have any chance of passing Lippo's tests. He is a Blacklist Hunter with a repertoire with includes the capture of Johness the Ripper: a famous mass murderer. In order to coerce prisoners to fight Hunter Exam candidates in the Trick Tower, he offers to shorten the sentence of any inmate by one year for every hour they stall the examinees.