In
The Wheel of Time, Myrddraal are a semi-synthetic race, born of
Trollocs and thus created second-hand by
Aginor. It is not exactly known why Myrddraal are born; the general explanation is that they are throwbacks to human gene pool in Trolloc stock, but that theory has some flaws. An alternate theory suggests that they may be Trollocs who can
channel.
Myrddraal are used as commands for Trollocs, as they are considerably smarter (or maybe sly would be the word) than Trollocs. But since Trollocs are such a untrustable folk, Myrddraal often, as precaution, somehow link Trollocs to them so that if Myrddraal died, Trollocs linked to it will die as well. This decreases the effectivity of army as killing Myrddraal can drop a whole unit down, but if not for this Myrddraal might as well eat their beloved leader in night hours.
Myrddraal are, as said, smart, and also very cruel. They don't have sense of humor, and their smile is only for intimidation, but they enjoy torturing people, be they humans or Trollocs.
Myrddraal have the shape of human and don't have all that strange stuff Trollocs often wear, even so that Myrddraal can be confused to human if it is sufficiently covered and you won't watch it move. They have gray, maggot-like skin and no eyes or hair. Despite this eyelessness, they can see quite well. It is believed to be some kind of force spun from Dark One.
Myrddraal have some strange abilities: Besides seeing with no eyes (and they do see in dark just as well as in light; light seems irrelevant to it, actually), their gaze (if you can call some pale ball with mouth moving into your direction a gaze) can cause fear in ordinary humans. Humans of powerful will can contain this fear, but normal people may just as well panic at sight. Myrddraal also can "jump" from shadows to shadows: Enter in one shadow and leave in other. It is not known how this works, or how far it can move, but this is something Aginor himself did not understand. It said he got thousands of Myrddraal killed trying to figure out how it works.
Myrddraal are generally described moving with viper-like grace, and they are competent swordsmen. The swords they wield are wrought in forges of Thakan'dar, and the metal they are made from has some qualities that cause them to be effectively very poisonous: A wound from Myrddraal blade is known to kill in hours, if not Healed with One Power.
Myrddraal are slow to die: if you cut a head off one, it will fall down and lose its ability to see (which would suggest their vision has something to with head, after all), but it will keep swinging its blade around and trash in ground for hours before admitting it's dead.
Thirteen channelers linked together, channeling One Power through Myrddraal can force any channeler into Shadow. This has not been observed and it is not known exactly what this means.