Illumi Zoldyck, yet another Zoldyck, which is the family who's known for being the best assassins in the world for hire. Illumi is Killua's oldest brother, and intensely powerful. He kills essentially any target, including other extremely high rated hunters, for cash.

Illumi is very intimidating for not giving a single shit. He rehearses and discusses with Hisoka about how something he's trying to stop from happening is Killua to accidentally kill his entire family and tens of thousands of people without breaking a sweat. He has a deep self-serving love for Killua to make sure his younger brother reaches his potential.

Illumi is a manipulator, using needles in himself or other targets to manipulate. He can force people to work for him so hard that they'll die of exhaustion, he can manipulate how he looks with disguises, and of course he can flat out create so much tension in people's muscles that they contract themselves to death.