Illumi Zoldyck (イルミ ゾルディック) is Killua's eldest brother. He is an experienced and expert assassin, whom along with his father was responsible for Killua's training and upbringing. Illumi is the most powerful among the Zoldyck siblings and a hard guy to deal with.

A certain amount of friendship is shared between Hisoka and Illumi, although it is unclear as to how it developed.

During the 287th Hunter's Exam, Illumi disguised himself as Gittarackur, using special pins to change his entire facial structure.

He is voiced by Urara Takano for the 1999 series and Masaya Matsukaze for the 2011 series.

Source:Wikipedia