A Lich (meaning “corpse”) is a powerful magical being striving for an eternal life, they bind their soul to their vast intellect allowing their soul to become immortal but their body dies and decays normally that’s why all Lich’s are either decaying humans or full blown skeletons.
A Lich is purely fiction but is based of certain Catholic Folklore, the word Lich is derived from the word “lychgate” which refers to a covered area at the entrance of a Cemetery where the casket awaits clergy before proceeding to have a proper burial. These skeletal monsters are of magical origin, each Lich formerly being a very powerful Magic-User or Magic-User/Cleric in life, and are now alive only by means of great spells and will because of being in some way disturbed
Lichs have had many years of experience with the Arcane Arts making them very powerful sorcerers and very patient. Their souls are immortal so the only way to immobilise them to destroy the body they posses but make sure your not to close otherwise you will become their new host body. They also have the power of Necromancy enabling them to raise and control lesser undead beings allowing them to have an army of the living dead.