It all began with a Tuphan sorcerer named Valikalen, who had come to fear death. Being a powerful noble, he had the money to indulge in queries with priests as well as seek out wise hermits to learn of ways to cheat death. A moderately moral man, he grew in wisdom and attracted a cult of like-minded followers who likewise sought a way to forever cheat death.
By means of elixirs and magic, Valikalen and his family were able to live unnaturally long lives. As some of the lesser cult members fell to the ravages of old age, they were embalmed and treated with spells that it was hoped would keep their souls from passing on to the afterlife. They became the first of the living dead; mummified zombies that were little more than walking shells. The living dead were confined to corridors of stone under the estate of Valikalen, lest they be discovered.
From the first undead, Valikalen began to learn of the importance of blood and organs to the undead. The mummified undead, with their organs removed, retained little of their soul and were but well-preserved shells of their former selves. While excellent servants, this fate was not Valikalen desired once his life force failed.
Even as these first steps were taken, some of Valikalen's followers reached the end of their natural lives. Unwilling to become mindless servants, many were forced to abandon their corrupted flesh, but lived on as spirits in the hopes that one day they could be returned to the flesh.
He did learn however, that by feeding blood to the living dead, it seemed to return some sentience to zombies and corporealness to ghosts, if only for a short while. Obviously, blood was somehow key to life itself, and Valikalen knew that his blood was even more powerful, for magic coursed through it.
As time passed, Valikalen learned new and startling techniques that slowly led him towards the discovery of immortality. First he learned that ghouls, the least of the intelligent undead, could retain their memories with a regular diet of living or freshly slain dead.
More experimentation led him to discover the next step up; by storing the removed organs in a solution of blood, a body could retain even more of its intellect and soul, becoming a mummy. The fresher the blood, the closer the mummy was in appearance to its living self, though the removal of the organs granted it some immunity to attack.
Eventually, Valikalen discovered the next evolution of undeath - the vampire. Though physically dead, by feasting on the blood of the living it could retain a semblance of life. However, for the foul crime of stealing life from others, the wrath of the sun god became the vampire's bane.
Immortality and death now loomed like dual specters before Valikalen. It was this that led to his final experiment, and perhaps the most powerful of undead - the liche. Valikalen became the first of his kind, and through his cult was able to elevate more into the ranks of lichdom by the benefit of their magic-heavy blood.
Eventually, the living no longer walked among the the Cult of the Everliving, and in undeath the cult descended into the catacombs beneath the estate, and outward in its need for the blood and flesh that kept its members alive.
From this cult has arose a society with a structured caste; at the lowest lies the mummified zombies and skeletons that make up the menial labor force - doomed to a mindless existance (some regressed from higher castes for crimes against the social order),
Next in stature are the desperate souls of the dead who seek a patron to bring them back to beings of flesh (often they act as messengers and scouts for a payment of blood to grant them corporeal pleasure if only for a short bit);
Then in stature come the ghouls, lower class individuals who are allotted a portion of flesh or blood to retain their conciousness as they flit about their undead lives;
Above such common dead can be found the mummies; those who while living possessed the money and/or power to have their organs properly preserved and kept soaked in the entrails of the living so that they retain the majority of their living memories
Near the top of the castes are the dreaded vampires; rare among the living dead for their ability to pass as the living, they can freely pass between the society of the dead and the living, secure with their wealth and power in the realm in the dead and capable of partaking from the living to feed themselves in the world above
And at the apex of the culture rule the liches. By the power of their magical blood they control and dispense bloody portions to the lower castes to keep the undead society from falling apart. They vie against each other for power, wealth and the control of the flow of blood. Many experiment with the creation of new and unique undead in pursuit of the continual adaption and evolution towards immortality without the need of bloody sustenance to retain their dark gift; others simply experiment for the joy of creating new and twisted life.