Illumi Zoldyck

Illumi wears unique, practical suits. Their main feature is that they allow for free movement. Furthermore, the clothes are often decorated with the very same pins he uses for his body manipulations.

Pinning (needle use). This is a key habit, closely tied to his Nen abilities. Illumi inserts special needles (often with a round head, yellow handle, and silver shaft) into his body to alter his appearance—his own or someone else's—and to modify his body structure, facial features, and even his voice. Removing the needles restores his original appearance. If he changes his appearance without the needles, the transformation lasts for about five hours, but his eyes remain unchanged. The actual insertion process is quite painful.
Manipulation. He actively uses his abilities to influence others—controlling living beings or even corpses.
Stealth. Illumi often disguises himself. A prime example is during the 287th Hunter Exam, where he hid under the identity of Gittaracura, completely altering his appearance with pins.

Illumi is a contradictory and rather dark character. Here's what's particularly noticeable about him:

Cool-headed and rational. His actions are almost always dictated by logic and expediency, not emotion.
Self-love and arrogance. He is convinced of his own exceptionalism. At the same time, he recognizes that his younger brother, Killua, is more gifted, and this has given rise to an obsessive-compulsive streak in Illumi—his goal is to control Killua.
Ruthlessness. Illumi has no regard for human life and is capable of killing on a whim, even those who trust him.
Stubbornness and persistence in achieving goals.
His relationship with his family is complex. On the one hand, he displays a twisted and overprotective love for Killua (for example, he implanted a needle in his brother's brain to prevent him from engaging in fights he knew he would lose—Illumi was trying to protect him). On the other hand, in certain situations (such as during internal family missions), he is willing to kill a relative. He is also willing to take responsibility for Alluka's power, even at the cost of his own life.

Build and height: tall, thin man.
Hair: very long, smooth, black. Usually combed back, but one strand is left uncovered. In her younger years, her hair was shorter—shoulder-length.
Eyes: large, black, without pupils.
Facial expressions: virtually nonexistent. When Illumi experiences emotion, only the width of his eyes changes.
Tattoo: She has a tattoo of a spider on her body. The number 11 is depicted on the spider's abdomen.