Lichdom

Liches are the remains of great wizards who embrace undeath as a means of preserving themselves. No wizard takes up the path to lichdom on a whim, and the process of becoming a lich is a well-guarded secret. It is believed that wizards that seek lichdom must make bargains with fiends, evil gods, or other foul entities, presumably demanding fealty and service for their knowledge.

A lich is created by an arcane ritual that traps the wizard’s soul within a phylactery. Doing so binds the soul to the mortal world, preventing it from traveling to the Outer Planes after death. While phylactery’s exist in the common space, the actual process to create them is unknown, as is the process of keeping it intact for the centuries of undeath the wizard is seeking.