Imhotep resurrecting and commanding his undead slaves.Kill them... and awake the others.
In fantasies and folklore, Liches are created when Necromancers, in their desire to obtain immortality, become powerful beings. They can also be created via Magic but are regarded as the most powerful of the Undead in fiction.
Liches can come in many forms; though the traditional Lich is a skeletal creature, Necromancers who take part of their bodies or souls and hide them away inside other people, items or a combination of both can be considered Liches - only by destroying the objects or individuals the Lich has hidden the parts of itself in can these Liches be destroyed, otherwise they will effectively return from any harm.
NOTE: Please do not add Necromancers to articles already listed under Liches as they are simply ascended Necromancers, much like how Archwizards are still a type of Wizards.