Mordeth is a minor antagonist of The Wheel of Time fantasy series by Robert Jordan.
Background
During the Trolloc Wars, Mordeth was a counselor to the ruler of Aridhol, a magnificent Ogier-built city. Because of his influence, Aridhol's methods at fighting the Shadow became as malevolent as the Shadow itself, only in a different way. The culmination was the destruction of the city. No enemy entered it, but every living creature in Aridhol, which later became known as "Shadar Logoth" ('the Place, where the Shadow waits'), was killed by the hate and evil that Mordeth spread. The evil councelor himself was spared, but he himself became a spirit, haunting the feared city (ruins) and waiting for a host to deceive and possess.
Role as an Antagonist
In the series, Mordeth first appeared in The Eye of the World when the main characters go to Shadar Logoth. He lures Rand al'Thor, Matrim Cauthon, and Perrin Aybara into an underground chamber full of cursed treasure. After a brief scuffle
Source:
http://en.wikipedia.org/wiki/Mordeth