The people's Lich. Those people are dead.
Kel’Thuzad’s origins remain shrouded in mystery. Indeed, even his original race remains uncertain. It is unknown if his wings are natural, the resort of some sort of experiment, or merely some sort of mutation. What is known is that he’s a fearsome and capable necromancer, capable of maintaining an army of dozens of undead at one time.
Recent events imply some sort of connection to the powerful necromancer, Malarath, although the nature of their relationship is not thought to be friendly. It is assumed that Kel’Thuzad may have learned necromancy from Malarath, given the rarity of the necromantic arts in this day and age, but whether Malarath himself directly taught Kel’Thuzad is still uncertain.
Although he initially appearing to have a cool demeanor, Kel’Thuzad is easy to anger, and prone to outbursts of powerful magic that destroys everything around him. This magic so fierce in nature that it often harms both him and his allies. How anyone has stayed around him despite these outbursts continues to be the biggest mysetery surrounding Kel’Thuzad, although it can be assumed that these people fear the consequences of abandoning him. As well they should.