Lich

A Lich is a powerful undead sorcerer who possesses tremendous magical power. Prior to his transformation into the Lich King, the Warchief of the Horde, Ner'zhul, had under his sway many Orcs who controlled various magical forces including Warlocks, Shamans and even some of the Death Knights created by Gul'dan in the aftermath of the First War. When these powerful individuals were captured along with Ner'zhul by Kil'jaeden and the Burning Legion the Eredar Lord twisted them into undead abberations and bound their will to that of Ner'zhul, who had been transformed into the soon to be infamous Lich King. As a reward for their loyalty, the Lich King gave all his Liches the power to control the furious icy elements of the north. Able to control the powers of frost along with their own considerable abilities in necromancy, Liches are considered to be some of the most powerful agents of the Scourge.

Not all Liches however, are former orcs. Many have been plucked from the ranks of humanity, offered immortality and power in exchange for their unwavering loyalty and obedience. The Archmage Kel'thuzad was one such convert, and several other Liches were created after him many of which who can trace themselves back to the Cult of the Damned.

Servants of the Scourge
During the reign of the Lich King, Liches were often placed as generals within the Scourge army, often acting as the voice of the Lich King himself during times of war. They are power-hungry, manipulative and vicious and they use their considerable abilities not only to serve their master the Lich King but also to undermine and often destroy other Liches, often through sabotage or political machinations. They resemble skeletons, but are often surrounded by a blue glow that radiates a constant chill and dress in long flowing robes, often adorned with gems and other precious metals.

A Lich may be raised from any mortal with significant magical ability and the willingness to serve the Lich King. While traditionally this translates into Necromancers there are some Shamans and Priests who have become Liches loyal to the Scourge throughout recent history.

Not all Liches however serve the Lich King or the Scourge. During the period of time in which Sylvannas Windrunner broke free of the Lich King's control, many of the Liches that were previously loyal to him did as well, with several changing their allegiance from the Scourge to the Burning Legion. This dissension was even further enhanced after the death of the Lich King at Icecrown Citadel when almost all intelligent undead were freed from the mental domination of the Lich King and were finally able to act on their own accord. While many have chosen to remain with the Cult of the Damned, others have become independent, working to further their own goals rather than the goals of any unseen master.

Killing a Lich: Phylacteries
In order to create a Lich the being who is making the transformation is required to bind his soul into a specific object. This object is known as a phylactery and is, at it's base form a soul battery through which a Lich can regenerate his physical form should it be destroyed in combat of any form. In order to permanently kill a Lich, the phylactery must also be destroyed for as long as it remains intact and undamaged the Lich will always be able to return to plague the land of mortals once more. To that end, a Lich is very careful about where his phylactery is located, and they will often go to great lengths to hide it as to ensure that it can never be destroyed.