Vyrko, God of Undeath and Witchcraft

Death is a topic which has, and will keep doing so until the eschaton, fascinated the minds of every culture. From the more carefree elves, to the war-like skågrom and beyond, death, tombs, death rites and more have been a crucial part of such cultures.
While the god of Life and Death, Tlacatl, and his multiple psychopomps are the first line of thinking for the religious questioning of such events, it is undeniable that a dark, unholy shadow looms around the issue. Walking, flesh-craving corpses, bone puppets animated through magic and the haunting souls of the killed have risen questions since the dawn of time.
While clerics of Tlacatl are able to manipulate the dead as a holy tool for good, it is undeniable that necromancy is an art that is often twisted to the darkest of purposes. While Arcana studies can allow a wizard limited power over undeath, historical examples of gigantic undead armies, magi able to live millenia and long-dead kings rising up from the grave suggest a stronger influence lurking beneath.
The myth of "Vyrko" is the most widespread answer; although such a term is an exaggeration. Vyrko is painted as a "god", a very specific and exclusive title, and of course, heresy of the largest deegree.

Current Understanding

While necromancers claim control over their shambling puppets, the truth is that any and all undead ultimately answer to the dark god Vyrko. Such a force is of course to be feared, but Vyrko uses his power for control very rarely. A necromancer understands that by binding an undead, they are signing a pact with the God of Undeath. Should their actions threaten his servants or his domain, the undead will turn on their masters and rip them to shreds.
This power however extends beyond the manipulation of dead flesh. The oft misidentified twin of necromancy is the rather broad term of “Witchcraft". While “witches" might get their powers from a variety of sources (Much like warlocks), true witchcraft, the one that implies the manipulation of one’s soul to apply curses and hexes also comes from this so-called god. 

The Animus Cage

Perhaps the most consistent myth regarding this creature is that of The Animus Cage. A powerful artifact designed by an ancient mage with the intention to forever trap souls for nefarious purposes. The cage was to be fitted around a victim’s head, trapping their soul. This was demonstrated for the first and last time on this forgotten mage’s apprentice. Vyrko, supposedly, felt the actions of the thaumaturge to be an affront to his power, so he possessed the girl and tore apart the evil spellcaster. The Cage was more powerful than anticipated, and Vyrko found himself partially trapped. As such, he moves around as the apprentice’s skeleton, with the Animus Cage still imprisoning her bleached skull. Since the trapping is not thorough, Vyrko is still able to reach outside and establish weak links with willing mortals, but his power has been diminished on the extreme.
When discussing sects and cults involved with this deity, it is good to be on the lookout for the symbol of the skeleton trapped within the Animus Cage: a circle or skull inside a cage, or crossed over by several bars. Occasionaly, humanoid skulls trapped inside cages have been used as holy symbols by priests of this evil entity.

Related Myths

There are multiple legends and stories which worshippers of this deity have linked to him. While this link is currently not proven, it would help explain a number of mysteries.
Perhaps the most prevalent of such stories is that of Liches and the similar Mummy Lords from the Sand Kingdoms. These undead do exist, although the complete process is unknown. Hundreds of hypotheses have been postulated, and it might as well be that a dozen are correct. Among those, the idea of lichdom as a reward from Vyrko has appeared time and time again in texts from his followers.
Another myth, probably of cognate origin with the skågrom mythology surrounding the death of a warrior and his return as an "einherjar", is that of a massive undead army hidden somewhere, ready to wreck havoc upon civilization on an apocaliptic event. Armies of undead acting with apparent intentionality but no apparent master have appeared before, such as in tales related to the Second War of Giants, were it is said that undead (Or einherjar by local denomination) aided the royal side in battle.

Divine Symbols & Sigils

A skull or circle, trapped inside a cage or crossed over with bars.
Small statuettes found sometimes include arcane runes inscribed on the bone, worms wriggling inside, jeweled eyes or other artistic liberties.

Divine Classification

God of Undeath and Witchcraft