In
The Wheel of Time,
Old Tongue for "the Hand of
Shadow". Also, a name with which an entity that resembles
Myrddraal is known with.
Shaidar Haran looks like your ordinary, run-of-the-mill Myrddraal, except that he (all Fades are male) is over 8 feet tall (or so, not sure about the exact number), while *all* ordinary Myrddraal are exactly the same height, which is about 6 or so feet. The Myrddraal don't have variation; one is pretty much the same as the other, for looks, height and all, which is why Shaidar Haran is pretty special.
He is special in other ways, too: He smiles. The Eyeless don't smile, ever; they don't have sense of humor. Even Trollocs have a sense of humor, if crude and violent; Fades don't.
But the most drastic strangeness about Shaidar Haran is his position. Usually, Fades are like lower officers: They command units, "fists" of Trollocs and act as messengers for important stuff for Shadow (their abilities with jumping in and out of shadows come handy in this). They rank higher than typical pledge-your-soul-to-Shadow, fodder-for-Trolloc-cookpot Darkfriends, but WAY lower than the Forsaken or some higher ranking DFs. Shaidar Haran, on the other hand, seems to be in some ways even higher than Forsaken themselves; upon visiting the Pit of Doom, in the test of Dark One's favor, in the tunnel which's ceiling's height depends on what DO thinks of you (if he's pissed off, you'll have to crawl on your belly, and usually even when he's not). Even Forsaken are made to (almost) crawl, yet Shaidar Haran may pass unhindered.
Shaidar Haran also seems to have some interesting tricks: he has been witnessed to block channeling, at least. But as a kickback, he seems to be somehow dependent on Shayol Ghul; he is unable to leave it for a long time. Shaidar Haran claims to speak with the mouth of Shai'tan himself.
From all this, the most popular theory is that Shaidar Haran is a bit modified Fade, boosted by powers from Dark One and is acting as DO's avatar as he himself can't *yet* enter the land himself (but has enough effect already to grant SH these powers). Other theories suggest SH to be resurrection of every Forsaken dead, most typically Ishamael or Lanfear. These theories seem unlikely, but you never know...