Lich are powerful mages who voluntarily seek out corruption by the Blood of the Gods, in order to extend their lives, gain greater power, continue their studies or further whatever their long-term private goals. A lich can only come about by the conscious choice and complex preparation of a very knowledgable and powerful Mage.
Lich have more control over their minds and personalities than most Blessed. However, as they must ritually consume the life force and mental energies of intelligent creatures in order to sustain themselves, suffice it to say that most Lich are as evil and selfish as any other Blessed.