A Lich is a sorcerer that usually willingly turns itself into an undead creature. Lichs look like a skeletal like creature and usually have their old cloths on, usually torn and ripped due to the fact that they have usually been around for a long time. They do this in order to obtain great dark powers, much stronger then a normal sorcerer or necromancer, also as an undead they will have alot more time to study. Lichs have the ability to control the undead, they can also make dead things into undead similar to a necromancer. It is also said that a lich can turn living creatures into undead without having to kill them first, although it is not completely certain.
this is a drawing I found on deviantart of a Lich