A human sorceror hungered for more power. He sacrificed his own life to move his soul into a more powerful vessel, an enchanted but lifeless skeleton. Combined, the being became known as Cairn.
Cairn has too many powers to list here, all based in his mystical abilities as a sorceror. He can conjure spirits, project blasts of energy, weave spells to effect one's mind, and worst of all is his knowledge of fiendgates (and how to open one).
Cairn wants nothing more than to unleash a horde of demons upon the Earth, and take his place as ruler of the ruined land. Lucky for us, opening a fiendgate requires more power than even Cairn wields, making it necessary to find another source of power (such as the rare gems known as ashstones).